With the increasing applications of ultra-high frequency (UHF) radio-frequency identification (RFID) in various fields that require rapid identification of a large number of tags, improving the throughput of RFID systems has become the research focus currently. By modulating tag signals to different Miller-subcarrier frequencies, the frequency division multiple access (FDMA) RFID system with$M$-values of 2 and 6 has been proposed. Furthermore, after analyzing the spectrum of the Miller-coded signal, the tag harmonic signal suppression algorithm, based on the Costas loop, has been proposed, which reconstructs the harmonic interference signal of the first channel and subtracts the interference in the second channel. The suppression performance of the algorithm can reach 14 dB and 11 dB through simulation and experiment. The reader that supports simultaneous query for tags has been designed and developed utilizing the Xilinx XC7Z020 chip and can successfully receive the tag signals in two channels.

As the use of ultrahigh frequency (UHF) radio-frequency identification (RFID) increases in various fields requiring the rapid identification of a large number of tags, research has shifted toward improving the access capacity of RFID systems. This article proposes a frequency division multiple access (FDMA) extension of conventional time division multiple access (TDMA) RFID systems by modulating tag signals to different Miller-subcarrier frequencies, achieving a theoretical throughput limit value of 0.9135 average successfully read tags per slot, which is 2.48 times that of the usually referred dynamic frame-slotted Aloha algorithm. The power spectral density (PSD) of Miller-modulated subcarrier (MMS) sequences is derived to uncover the tag interference caused by the modulation signal sidelobe power within each subchannel. After that, a successive interference cancellation (SIC) scheme is employed in a four-tag signal reception situation, enhancing the simultaneous tag replies interference suppression and achieving a small performance deterioration if compared with a conventional TDMA system. An experimental analysis is also described to show the feasibility of the proposed FDMA extension of TDMA-based UHF RFID systems.

How to obtain the information from massive tags is a key focus of RFID applications. The occurrence of collisions leads to problems such as reduced identification efficiency in RFID networks. To tackle such challenges, most tag collision arbitration protocols focus on scheduling tag identification with collision avoidance. However, how to effectively identify tags in collisions to improve identification efficiency has not been well explored. In this paper, we propose a group query allocation method to divide the string space into mutually disjoint subsets which contains several strings. Each string can be viewed as a full ID or partial ID of a tag. When multiple string from a subset are sent simultaneously, the reader can identify all of them in a time slot. Based on the group query allocation method, a segment detection based characteristic group query tree (SD-CGQT) protocol is presented for fast tag identification by significantly reducing the collision slots and transmitted bits. Numerous experimental results verify the superiority of the proposed SD-CGQT, compared to prior arts in system efficiency, total identification time, communication complexity and energy consumption.

This article describes the design of a hydrogen concentration monitoring system based on ultrahigh-frequency radio-frequency identification (RFID) passive tags, which adopts ISO/IEC 18000-6 Type C standard. Tag devices have been designed by employing a microcontrol unit, making the proposed solution very suitable for low-cost hydrogen concentration measurement in wireless sensor networks. Furthermore, anti-collision capability has been realized by implementing a new true random number generator based on the hydrogen concentration sensing circuit and analog-to-digital converter, without employing any additional device. The correctness of all operations of the RFID system has been experimentally verified in a multiple-tag environment, as well as the hydrogen concentration monitoring capability. Particularly, measurement on an RFID tag prototype developed for the bandwidth 920-925 MHz has revealed that when the ambient temperature is 25 °C and humidity 80%, a maximum error of 9.8% is found within a hydrogen concentration range from 0.24% to 2.4%.

Efficient and effective objects identification using radio frequency identification (RFID) is always a challenge in large-scale industrial and commercial applications. Among existing solutions, the tree-based splitting scheme has attracted increasing attention because of its high extendibility and feasibility. However, the conventional tree splitting algorithms can only solve tag collision with counter value equals to zero and usually result in performance degradation when the number of tags is large. To overcome such drawbacks, we propose a novel tree-based method called fast splitting algorithm based on consecutive slot status detection (FSA-CSS), which includes a fast splitting (FS) mechanism and a shrink mechanism. Specifically, the FS mechanism is used to reduce collisions by increasing commands when the number of consecutive collision is above a threshold, whereas the shrink mechanism is used to reduce extra idle slots introduced by the FS. Simulation results supplemented by prototyping tests show that the proposed FSA-CSS achieves a system throughput of 0.41, outperforming the existing ultra high frequency RFID solutions.