Modulation order selection and power allocation for energy efficient VLC-OFDM systems

In this paper, we investigate the modulation order selection and power allocation for energy efficient (EE) orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) systems. Unlike the widely studied Gaussian inputs, we consider that each subcarrier has discrete modulation scheme inputs. Under the constraints of the maximum total transmission power and the minimum spectral efficiency (SE), we formulate the EE optimization problem with respect to the modulation order and the power of the subcarriers. Utilizing the intrinsic lowpass characteristic of the VLC channel, we propose an iterative search method to solve the problem efficiently. Simulation results show that, compared with traditional modulation order selection and power allocation method, in our method, the number of subcarriers using high order modulation is less and the total transmission power is lower, which leads to a higher energy efficiency.