Abstract
Driven by the limited radio spectrum resources and the high energy consumption of wireless devices, symbiotic radio (SR) has recently been proposed to support passive Internet-of-Things (IoT) networks, where a primary transmitter (PT) transmits information to a primary reader (PR), while passive backscatter devices (BDs) modulate their own information on the received primary signal and backscatter the modulated signal to the same PR by adjusting their reflection coefficients. Existing works on SR have mainly studied the case of a single BD while without considering the BD's energy harvesting (EH) ability. In this paper, we aim to maximize the energy efficiency (EE) of an SR system that includes multiple BDs each being able to harvest energy while backscattering, by jointly optimizing the PT transmission power and the BDs' reflection coefficients and time division multiple access (TDMA) time slot durations for both the parasitic SR (PSR) and commensal SR (CSR) cases. To solve the formulated non-convex optimization problems, we propose a Dinkelbach-based iterative algorithm that builds on the block coordinated decent (BCD) method and the successive convex programming (SCP) technique. Simulation results show that the proposed algorithm converges fast, and the system EE is maximized when the BD that can provide the highest EE is allocated the maximum allowed time for backscattering while guaranteeing the throughput requirements for both the primary link and the other backscatter links.
Highlights
I T is predicted that the Internet of Things (IoT) devices will be over 80 billion worldwide by 2030 [1], putting huge pressure on wireless networks concerning the limited radio spectrum resources and soaring energy consumption
Since the backscatter devices (BDs) have no knowledge of the information transmitted by the primary transmitter (PT), the EE of backscatter communications (BackCom) will be limited by the strong interference caused by the PT [6]
Denote the primary signal transmitted from the PT by s(n) with symbol period of Ts and the ith BD’s signal by ci(l) with symbol period of Tc, where n and l are the indices of symbols of the primary signal and the BackCom signal, respectively
Summary
I T is predicted that the Internet of Things (IoT) devices will be over 80 billion worldwide by 2030 [1], putting huge pressure on wireless networks concerning the limited radio spectrum resources and soaring energy consumption. We formulate an optimization problem to maximize the EE of the SR system by jointly optimizing the PT transmission power and the BDs’ reflection coefficients and TDMA time slot durations for both the PSR and CSR cases. The simulation results show that the proposed algorithm converges very fast and the system EE is maximized when the BD that can contribute the most toward the system EE is allocated the maximum allowed time to backscatter its information to the PR while the other BDs’ throughputs being kept at the minimum required level This best BD is determined by the optimized PT transmission power in the corresponding time slot. We introduce the SR network with multiple BDs, present the throughout analysis for both the PSR and CSR cases, and define the system EE of the network
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