Mutualistic Relaying NOMA Transmission for Green Cellular IoT With Backscatter Sensors

Backscatter communication-aided nonorthogonal multiple access (BAC-NOMA) is a potential enabling technology for realizing green cellular Internet of Things (IoT). However, in BAC-NOMA-based relaying systems, the mutualistic mechanism between backscatter sensor nodes (BSNs) and cellular users remains unclear, and the complex composite channels pose a challenge to precisely characterize theoretical performance. Therefore, this article proposes a mutualistic BAC-NOMA scheme and a bidirectional mutualistic BAC-NOMA (BMBN) scheme for the relaying system with a single BSN and multiple BSNs, respectively. In the considered system, one base station (BS) serves two cell-edge users via a decode-and-forward (DF) relaying user, while BSNs transmit their information to the BS using cellular radio frequency (RF) signals and backscatter modulation. To accurately evaluate the system performance, we employ the Gamma-Gamma distribution based on channel parameter transformation, as well as the Meijer G-function and Gaussian-Chebyshev quadrature, to derive the closed-form expressions for the ergodic sum capacity (ESC), capacity scaling, and energy efficiency (EE). The simulation results verify the correctness of the theoretical analysis and demonstrate the performance advantages of the proposed schemes compared with the conventional orthogonal multiple access (OMA) and DF relaying NOMA (DFR-NOMA) schemes.