Hybrid Visible Light and Radio Frequency Communication Systems

In this paper we propose a hybrid visible light communications (VLC) and radio frequency (RF) femtocell system and investigate user association issues to achieve effective load balancing. We propose a scheme for cell association based on the minimum distance to the closest access point (AP) which involves a simple and fully uncoordinated decision. The performance of the three tier (macro-, femto- and optical attocells) heterogeneous network is analysed in terms of area spectral efficiency (ASE). We compare the performance of the minimum distance user association, the maximum signal to interference and noise ratio (SINR) based association and a decentralized iterative algorithm. The latter scheme results in a near optimal solution by considering the load of the AP in the cell association process. Simulation results show that the simple min-distance based user association nearly achieves the optimal load-aware performance. Moreover the average ASE of the hybrid VLC/RF system may be increased by at least two orders of magnitude over the stand-alone RF network.