  The coexistence of radio frequency (RF) and visible light communications
(VLC) in typical indoor environments can be leveraged to support vast user
quality-of-service (QoS) needs. In this paper, we target a hybrid RF/VLC
network in which data transmission is provided via either an RF access point or
a VLC luminary based on a selection process. We employ the concept of effective
capacity, which defines the maximum constant arrival data rate at the
transmitter buffer when the QoS needs are imposed as limits on the buffer
overflow and delay violation probabilities, as the main selection criteria. We
initially formulate the effective capacity of both channels with respect to
channel gains and user distribution. Under the assumption of uniform user
distribution within the VLC cell, we then provide a closed-form approximation
for the effective capacity of the VLC channel. We further investigate the
effects of illumination needs and line-of-sight blockage on the VLC
performance. In addition, we explore the non-asymptotic bounds regarding the
buffering delay by capitalizing on the effective capacity. Through simulation
results, we show the impacts of different physical aspects and data-link QoS
needs on the effective capacity and delay bounds.
