Scalable Multi-BD Access for OFDM-Based Symbiotic Backscatter Communications

Abstract

We propose an interference-free multi-backscatter device (BD) access scheme for orthogonal frequency division multiplexing (OFDM)-based symbiotic backscatter communication (SBC). Specifically, we introduce an orthogonal frequency-code spread (OFC) scheme in which the transmitter reserves empty subcarriers for BDs to incorporate their information through frequency shifting, which effectively suppresses direct-link interference (DLI). Since enabling simultaneous access over shared subcarriers introduces inter-backscatter device interference (IBDI), a blockwise orthogonal code-spread is applied to assign each BD to a unique codeword, thereby mitigating IBDI with orthogonal transmissions of all BD signals in the code domain. We develop a non-coherent energy detector whose performance is analyzed in terms of average probability of missed detection (PMD) and sum-rate under Rayleigh fading. The simulation results validate the OFC scheme and demonstrate low PMD values and high spectral efficiency compared to conventional code-assisted multiple-BD access schemes.