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

• Published in: IEEE transactions on communications Vol. 67; no. 3; pp. 2157 - 2172
• Main Authors: Soltani, Mohammad Dehghani, Purwita, Ardimas Andi, Zhihong Zeng, Haas, Harald, Safari, Majid
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Accuracy; Approximation; device orientation; Earth; Electronic devices; fading; Handover; Incidence angle; Laplace distribution; Light fidelity; light-fidelity (LiFi); Line of sight; Mathematical analysis; Mobile communication systems; Optical wireless communications; Orientation; Probability density function; Probability density functions; random waypoint; receiver rotation; Receivers; Signal processing; Systems analysis; Trigonometric functions; Wireless communication; Wireless communications; Wireless networks
• DOI: 10.1109/TCOMM.2018.2882213
• ISSN: 0090-6778

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 orientation-based 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.