  Ambient backscatter communication (AmBC) has been introduced to address
communication and power efficiency issues for short-range and low-power
Internet-of-Things (IoT) applications. On the other hand, reconfigurable
intelligent surface (RIS) has been recently proposed as a promising approach
that can control the propagation environment especially in indoor communication
environments. In this paper, we propose a new AmBC model over ambient
orthogonal-frequency-division-multiplexing (OFDM) subcarriers in the frequency
domain in conjunction with RIS for short-range communication scenarios. A tag
transmits one bit per each OFDM subcarrier broadcasted from a WiFi access
point. Then, RIS augments the signal quality at a reader by compensating the
phase distortion effect of multipath channel on the incident signal. We also
exploit the special spectrum structure of OFDM to transmit more data over its
squeezed orthogonal subcarriers in the frequency domain. Consequently, the
proposed method improves the bit-error-rate (BER) performance and provides a
higher data rate compared to existing AmBC methods. Analytical and numerical
evaluations show the superior performance of the proposed approach in terms of
BER and data rate.
