Abstract
Visible light communications (VLC) are proposed for increasing the spectral efficiency and the number of devices served in indoor environments, while providing illumination through light emitting diodes (LED). For VLC, each optical access point (AP) provides a small and confined area of coverage. Since several sources of light are usually deployed in overlapping fashion in order to provide satisfactory illumination, VLC are limited by inter-cell interference. Moreover, transmission from a specific optical AP can be blocked by the elements of the scenario. On the other hand, radio-frequency (RF) systems such as WiFi are usually available in most of the indoor scenarios. In this work, we first propose a dynamic cell formation method for grouping the optical APs in multiple optical cells that cover a footprint each minimizing the inter-cell interference. After that, we use transmission based on blind interference alignment (BIA) in each optical cell. Considering the coexistence with RF systems based on orthogonal frequency division multiplexing (OFDM), a load balancing algorithm is proposed for managing the resources of the resulting hybrid VLC/RF network and determining the user association to each system. However, the complexity of this optimization problem is excessively high for practical VLC/RF networks. In order to obtain a suboptimal but tractable solution, we propose a decentralized optimization method based on Lagrangian multipliers. Simulation results show that the proposed scheme outperforms other approaches for user grouping and managing the resources of hybrid VLC/RF networks.
Highlights
The continuous demand on wireless data traffic makes the use of new spectrum beyond the tradicional radio-frequency (RF) bands a requirement for providing high data rates while supporting an exponentially increasing number of users [1]
We focus on a transmission scheme referred to as blind interference alignment (BIA) that provides a growth of degrees of freedom (DoF) without the need for channel state information at the transmitter (CSIT) as the number of users increases [10]
The proposed dynamic cell formation for Visible light communications (VLC) based on BIA provides greater DoF and user-rate than other approaches such as static cell formation or assuming full connectivity among all the optical access point (AP) to each user
Summary
The continuous demand on wireless data traffic makes the use of new spectrum beyond the tradicional radio-frequency (RF) bands a requirement for providing high data rates while supporting an exponentially increasing number of users [1]. Motivated by [19], we consider a topological approach in which the optical APs are grouped in elastic cells from a user-centric perspective For this approach, we assume that transmission in the VLC system employs the BIA scheme while the RF system is based on OFDM. The optical APs can be grouped forming optical cells serving to a set of users in order to manage the interference We assume that both systems do not have CSIT nor data sharing or cooperation exist among the optical APs. The knowledge of the central unit is limited to the network topology and the coherence time. The average movement of the users corresponds to a speed of 3 Km/h
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