Joint Power and Time Allocation of Pilot Scheme Selection for Uplink mMTC in ITSN

Integrated terrestrial-satellite networks (ITSN) is regarded as an effective solution to enable ubiquitous connectivity for massive machine type communications (mMTC) in the next generation of mobile system. In this paper, we study an uplink code-domain non-orthogonal multiple access (CD-NOMA) mMTCs system for ITSN. Considering that the conventional orthogonal pilot (OP) scheme is inefficient due to allocate dedicated time slot for pilot sequences, especially when the length of pilot sequences is large and need allocated more time slot for pilot transmission, the residual time slot for data offloading need consume more energy. To address this challenge, the power and time allocation is jointly optimized to reduce the energy consumption. Closed-form expressions for the joint optimal power and time allocation solutions are obtained, and used to establish the conditions for determining whether the OP scheme, superimposed pilot scheme, or hybrid pilot scheme should be used for mMTC. Simulations are provided to confirm the reliability of our analytical results and show the impact of various parameters on the system performance.