Achieving Multistate Vector Scattering with Unmodified Digital Input/Output Pins

This paper studies the potential of multistate vector scattering using configurable general purpose input/output (GPIO) pins commonly present on digital devices. A low-cost EFM8BB1 microcontroller and its development board is studied to explore the possible signaling constellations. This specific microcontroller architecture is a modeled after the Intel 8051 and presents a variety of configuration options for digital GPIO pins. This work measures impedances of 32 possible GPIO configurations, and designs a quaternary over-the-air signaling scheme that transmits two bits per symbol period. This study and experimental proof-of-concept is performed at the UHF RFID band (915 MHz). This work demonstrates that multistate scattering without modification is possible, although with performance limitations that are discussed.