Energy-Spectral Efficiency Tradeoff in DCO-OFDM Visible Light Communication System

Due to its simple implementation and higher spectral efficiency (SE), the direct current (DC) biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme has been extensively employed in visible light communication (VLC) system. In this paper, the tradeoff between energy efficiency (EE) and SE in DCO-OFDM system is investigated. Specifically, the achievable SE of DCO-OFDM system with power and bit loading is derived, and the closed-form expression of the EE-SE tradeoff is obtained, on the basis of which, the optimal SE to maximize EE is derived, and the optimal parameters of the DCO-OFDM system, e.g., the horizontal and vertical distances of optical transmission network, the number of subcarriers, to maximize the EE-SE tradeoff are theoretically derived. Moreover, to derive the optimal transmitted power, a Pareto optimal set based multi-objective optimization (MOO) is formulated, which is successfully transformed into a single-objective optimization (SOO), with the help of a proposed EE-SE tradeoff metric. Finally, simulation results are provided to verify the presented EE-SE tradeoff, the derived optimal SE, the optimal vertical distance of optical transmission network and the optimal transmitted power.