Performance Analysis of Uplink Uncoordinated Code-Domain NOMA for SINs

Space information networks (SINs) are regarded as an effective solution to enable a broadband access capability in a global coverage and cost-effective manner for massive machine type communications (mMTC). A collision often occurs when two or more user equipments (UEs) select the same pilot in mMTCs, and the received colliding signals are treated as interference. In this paper, we first analyze the problem of pilot collision for uplink mMTCs in SIN, then we investigate the performance of an uncoordinated code domain non-orthogonal multiple access (NOMA) protocol. Moreover, to recover the information in collisions, we adopt successive interference cancellation (SIC) and successive joint decoding (SJD) under a shadowed-Rician fading and path loss satellite-ground channel model, and derive the expressions of the outage probability and maximum system throughput for SIC and SJD, respectively. Numerical and simulation results validate our analytical results and show that the maximum system throughput of SJD is almost double that of SIC.