Metasurface Direct Antenna Modulators in non-Line of Sight Channels for the Internet of Things

A Direct Antenna Modulation (DAM) transmitter is modelled in wideband channels using Direct Sequence Spread Spectrum (DSSS) as a low-cost, low-complexity solution for the Internet of Things (IoT). Metasurface-based DAM is an emerging technique where a baseband signal is modulated directly onto a radio frequency (RF) carrier wave using a reconfigurable metasurface. This technique removes the requirement of the power amplifier (PA) to amplify complex modulated signals, allowing the use of a simple, energy efficient PA to amplify only the carrier wave. The reduction in power consumption and RF electronics makes DAM an attractive low-cost, low-complexity transmitter technology. This paper discusses the use of a DAM transmitter as an IoT access point transmitter using DSSS to overcome broad-band fading and mitigate the systematic distortion inherent in the technique. Simulation shows DAM to have negligible impairment in 3GPP urban channels compared with ideal modulation when balanced spreading codes are used.