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Superimposed Pilot Code-Domain NOMA Scheme for Satellite-Based Internet of Things

Satellite-based Internet of Things (S-IoT) is regarded as an effective solution to enable ubiquitous connectivity in a global coverage and cost-effective manner for massive machine type communications (mMTC) in the future Internet of Things. In this article, we propose a superimposed pilots code domain nonorthogonal multiple access over a shadowed-Rician fading and path loss satellite-ground channel model in uplink mMTC S-IoT system. First, we analyze the interference due to the collision in the random access scenario, and propose an iteration channel estimation based on ridge regression algorithm to attain a more precise channel state information. Moreover, we utilize successive interference cancellation (SIC) and successive joint decoding (SJD) to recover the singleton user equipments. Then, we derive the expressions of the outage probability and maximum system throughput of SP scheme, and compared with the regular orthogonal pilot (RP) scheme under SIC and SJD, respectively. Simulations validate our analytical results and show that the achievable system throughput of the SP scheme under SJD can outperform that of the RP scheme in a S-IoT system for short packet transmission.