Bidirectional Optical Spatial Modulation for Mobile Users: Toward a Practical Design for LiFi Systems

Abstract

Among the challenges of realizing the full potential of light-fidelity (LiFi) cellular networks are user mobility, random device orientation and blockage. In the paper, we study the impact of those challenges on the performance of LiFi networks in an indoor environment using measurement-based channel models, unlike existing studies that rely on theoretical channel models. In our work, 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, e.g., the screen of a smartphone, 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. In fact, we show that MDR outperforms SR by over 10 dB at bit-error ratio (BER) of 3.8×10 −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 we apply the same techniques 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. Furthermore, 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.

Physical Layer Security for Visible Light Communication Systems: A Survey

“…When the communication link is interrupted by blockers, adding extra power cannot compensate for the data loss. Solutions to simplify the effect of link blockage were introduced in [136], [153], [154]. A multi-directional receiver (MDR) for which PDs are located at different sides of a smartphone is introduced in [136], [153] and has been assessed in the presence of link blockage, user mobility as well as device random orientation.…”

“…Solutions to simplify the effect of link blockage were introduced in [136], [153], [154]. A multi-directional receiver (MDR) for which PDs are located at different sides of a smartphone is introduced in [136], [153] and has been assessed in the presence of link blockage, user mobility as well as device random orientation. It is denoted that the MDR structure outperforms the conventional configuration for which all PDs are placed on one side of a smartphones, for example on the screen side.…”

Exploiting Blockage in VLC Networks Through User Rotations

“…This topic is only explored to a small extent in literature. The authors in [13] analyze the impact of blockage on the bit error rate and the signal-to-noise ratio. The work in [14] investigates the effect of blockage on the outage probability considering different blockage densities.…”

Impact of Device Orientation on Error Performance of LiFi Systems

“…It is shown that the polar angle can be modeled by either the Laplace distribution (for static users) or the Gaussian distribution (for mobile users) while the azimuth angle follows a uniform distribution. Solutions to alleviate the impact of device random orientation on received SNR and throughput are proposed in [20]- [22]. In [20], the statistics of Euler rotation angles are provided based on the experimental measurements.…”

“…Solutions to alleviate the impact of device random orientation on received SNR and throughput are proposed in [20]- [22]. In [20], the statistics of Euler rotation angles are provided based on the experimental measurements. Then, simulations of BER performance for spatial modulation using a multi-directional receiver configuration with consideration of random device orientation is evaluated.…”