With the explosive growth of the data traffic and the access number of intelligent devices, the wireless communication systems based on the radio frequency (RF) is suffering from the pressure of spectrum shortage and access congestion constantly, which can be alleviated with the help of visible light communication (VLC). However, due to the limitations of VLC such as finite coverage and inconvenient uplinks, it is imperative to form the hybrid systems and realize the complementary advantages of VLC and RF. In this paper, the hybrid VLC-RF system with multi-users is investigated, where the sum achievable rate and energy efficiency (EE) are maximized via the alternate optimization of transceiver association and power allocation. In addition, based on various types of multiple access points, EE is optimized under different QoS requirements for green communications. With the assistance of proper approximations, the overall problem is decomposed into several convex sub-problems, which can be solved analytically and avoid traversal permutation. The numerical simulations show the effectiveness and scalability of the proposed algorithm in the hybrid VLC-RF system, which can achieve superior performances than the conventional methods and single systems in multifarious scenarios.

Visible light communication (VLC) is one of the candidates to realize data rates of up to tera-bps in indoor scenarios, and is a popular topic in Internet of Things (IoT) applications. However, the receiving performance of the VLC channel is affected by relative locations of transceivers directly, while the uniform illumination is also required when the IoT devices can appear anywhere with strong mobility. Consequently, both the illumination uniformity and the average achievable rate are optimized by joint lamp arrangement and power allocation in this article. Moreover, the achievable rate maximization under diverse uniformity constraints is also obtained based on different room sizes and various numbers of lamps. The feasibility and superiority of the proposed algorithms are demonstrated by simulation validations, while the lower and upper bounds of uniformity constraints are explored. Numerical results also show the changing tendency of average achievable rates in multifarious situations, and the proposed schemes realize the tradeoff between uniform illumination and communication performance.

Visible light communication (VLC) has gradually gained increasing attention in recent years, but new researches are still needed for conventional technologies in the VLC system, as the visible light signal must be real-valued and non-negative, and it is transmitted over the specific ergodic channel. In this paper, the definition of ergodic optical channel is firstly proposed, and the coded modulation average mutual information (CMAMI) of the VLC system is investigated under both fixed and ergodic optical channels. The gradient descent (GD) algorithm for constellation optimization of amplitude-phase modulation (APM) symbols is adopted, while the improved method for GD based on central symmetry is also proposed to accelerate the convergence for higher order constellations. The numerical simulation proves that the VLC system with optimized constellations can reach larger CM-AMI based on asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) compared with quadrature amplitude modulation (QAM) systems, and the influence of the ergodic optical channel is also evaluated.