Minimizing Total Transmission Time in Hybrid Active-Passive Mutualistic Symbiotic Radio

The hybrid active-passive mutualistic symbiotic radio can address the low transmission rate of the secondary user (SU) in the traditional mutualistic symbiotic radio, but the transmission delay, which is very critical for time-sensitive Internet of Things, has been overlooked, and its transmission performance is limited at a low primary user’s (PU’s) transmit power. In this letter, we propose a new transmission time scheduling structure that consists of pure energy harvesting (EH), backscatter communication (BC) and active communication (AC) phases, rather than only containing BC and AC phases in the previous work, and formulate a non-convex problem to minimize the total transmission time of all SUs. Employing successive convex approximation (SCA) and auxiliary variables, the original problem can be transformed into a convex one, then a SCA-based iterative algorithm is proposed to solve it. It is found that for minimizing the total transmission time, at least one SU consumes all harvested energy in each transmission block while maintaining its throughput at a minimum required level. Simulation results validate the swift convergence of the proposed iterative algorithm and the superior performance of our proposed transmission time scheduling structure at a low PU’s transmit power, compared to the existing ones in terms of the total transmission time of all SUs and the feasible region of the PU’s transmit power.