  Among the challenges of realizing the full potential of light-fidelity (LiFi)
cellular networks are user mobility, random device orientation and blockage. We
study the impact of those challenges on the performance of LiFi in an indoor
environment using measurement-based channel models. We adopt spatial modulation
(SM), which has been shown to be energy efficient in many applications,
including LiFi. We consider two configurations for placing the photodiodes
(PDs) on the user equipment (UE). The first one is referred to as the screen
receiver (SR) whereby all the PDs are located on one face of the UE, whereas
the other one is a multi-directional receiver (MDR), in which the PDs are
located on different sides of the UE. The latter configuration was motivated by
the fact that SR exhibited poor performance in the presence of random device
orientation and blockage. We show that MDR outperforms SR by over $10$ dB at
BER of $3.8\times10^{-3}$. Moreover, an adaptive access point (AP) selection
scheme for SM is considered where the number of APs are chosen adaptively in an
effort to achieve the lowest energy requirement for a target BER and spectral
efficiency. The user performance with random orientation and blockage in the
whole room is evaluated for sitting and walking activities. For the latter, we
invoke the orientation-based random waypoint (ORWP) mobility model. We also
study the performance of the underlying system on the uplink channel where the
same techniques are used for the downlink channel. Specifically, as the
transmitted uplink power is constrained, the energy efficiency of SM is
evaluated analytically. It is shown that the multi-directional transmitter
(MDT) with adaptive SM is highly energy efficient. As a benchmark, we compare
the performance of the proposed framework to that of the conventional spatial
multiplexing system, and demonstrate the superiority of the proposed one.
