Design and development of a passive computational UHF RFID platform using vector backscatter modulation on the uplink

Resumen

This work presents the steps taken to design and implement a passive, computational Ultra High Frequency (UHF) Radio Frequency Identification (RFID) platform using vector backscatter modulation to increase the data throughput on the reader-to-tag communication link. Passive UHF RFID represents an automated identification technology operating in the Industrial Scientific and Medical (ISM) band between 860 MHZ and 960 MHZ. One such RFID system consists of an interrogator (reader) and at least one wirelessly powered transponder (tag). The energy needed for the operation of the tag is harvested from the incident electromagnetic wave. After the reader has interrogated the tags, the reader radiated continuous wave is used as the carrier for the tag-to-reader backscatter communication. This technology uses antenna load modulation to reflect a distinct part of the incident wave corresponding to the transmitted data sequence. Due to recent advances in the area of RFID, transponders are no longer used for identification only. With the availability of low-power sensors and microcontroller units (MCUs), sensoric and computational capabilities have been added to attract a wider field of applications. The additional need of being able to backscatter the data collect by a sensor, or computed by the MCU to the reader requires further advances considering the backscatter communication link. As part of this thesis we have presented a thorough study of State-of-the-Art passive computational RFID. This theoretical and experimental investigation of the performance limitations, has fruited in the identification of gaps considering the typically used impedance measurement methodologies. Thus, we have proposed an alternative method for measuring the chip impedance of an UHF RFID chip, as well as an alternative approach to measuring the reflected harmonic power using a Digital Sampling Oscilloscope. As a result, the reflected harmonics at low input power levels could be neglected when designing the presented modular passive UHF RFID platform with easily exchangable modules. This research platform facilitates the design process when developing novel UHF RFID solutions. The further proposed passive computational UHF RFID platform using backscatter communication represents a complete RFID system consisting of a tag with the ability to transmit 2 bits at a time and a Software Defined Radio reader being able to demodulate the tag response.