Modeling the Random Orientation of Mobile Devices: Measurement, Analysis and LiFi Use Case

Abstract

Light-fidelity (LiFi) is a networked optical wireless communication (OWC) solution for high-speed indoor connectivity for fixed and mobile optical communications. Unlike conventional radio frequency wireless systems, the OWC channel is not isotropic, meaning that the device orientation affects the channel gain significantly, particularly for mobile users. However, due to the lack of a proper model for device orientation, many studies have assumed that the receiver is vertically upward and fixed. In this paper, a novel model for device orientation based on experimental measurements of 40 participants has been proposed. It is shown that the probability density function (PDF) of the polar angle can be modeled either based on a Laplace (for static users) or a Gaussian (for mobile users) distribution. In addition, a closed-form expression is obtained for the PDF of the cosine of the incidence angle based on which the line-of-sight (LOS) channel gain is described in OWC channels. An approximation of this PDF based on the truncated Laplace is proposed and the accuracy of this approximation is confirmed by the Kolmogorov-Smirnov distance. Moreover, the statistics of the LOS channel gain are calculated and the random orientation of a user equipment (UE) is modeled as a random process. The influence of the random orientation on signal-to-noise-ratio performance of OWC systems has been evaluated. Finally, an orientationbased random waypoint (ORWP) mobility model is proposed by considering the random orientation of the UE during the user's movement. The performance of ORWP is assessed on the handover rate and it is shown that it is important to take the random orientation into account.

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

“…The measurement results in Table I show that the coherence time for the orientation angles are on the order of several hundred milliseconds, and we assume that the coherence time for the channel matrix is also similar. This was confirmed in [20]. Therefore, it can be assumed that the channel gains are known for each transmitted data block of length smaller than the channel coherence time.…”

“…Measurements were recorded for static and mobile users (sitting and walking activities, respectively). More details about the data measurement can be found in [20].…”

“…Note that R α ( Tc,α Ts ) = 0.05 where T c,α is the coherence time of α and T s is the sampling time [20]. Using the above equations:…”

“…An orientation-based random waypoint (ORWP) mobility model is introduced in[20], where the elevation angle of the UE is included during user's movement. An altered version of ORWP (where Algorithm 1 Orientation-based random waypoint (ORWP) 1: Initialization: n ←− 1; k ←− 1;Denote P n = (x n , y n ) and P 0 = (x 0 , y 0 ) as the nth and initial UE's positions, respectively; N as the number of simulation runs; v as the average speed of UE; T c,α , T c,β and T c,γ as the coherence time of α, β and γ, respectively; Set T c = min{T c,α , T c,β , T c,γ }; µ α , µ β and µ γ as the mean and σ 2 α , σ 2 β and σ 2 γ as the variance of Gaussian RPs α, β and γ; 2: for n = 1 : N do 3:…”

Physical Layer Security for Visible Light Communication Systems: A Survey

“…Based on the above discussion, re-investigating the secrecy performance of VLC systems by considering the aforementioned measurement-based channel models and mobility models presents an interesting future research direction, since it helps to develop adequate PLS techniques for VLC systems in practical and real-life scenarios. Furthermore, in order to analyze the performance of mobile users more realistically, an orientation-based RWP (ORWP) mobility model was first proposed in [135] and then extended in [136]. The ORWP model provides a more realistic framework for performance evaluation of mobile users in VLC systems by incorporating the orientation of the device and the mobility of the user.…”