[Paper Review] Physical Layer Performance Evaluation of Wireless Infrared-based LiFi Uplink

Cheng Chen, Dushyantha A. Basnayaka+3 more|arXiv (Cornell University)|Apr 30, 2019

Optical Wireless Communication Technologies24 references4 citations

TL;DR

This paper presents an analytical framework for evaluating the physical layer performance of wireless infrared-based LiFi uplink systems, accounting for user equipment randomness, orientation, path loss, and blockage. It derives accurate statistical models for optical channel path loss and SNR, demonstrating that up to 250 Mbps average data rate is achievable with commercial front-end components under realistic indoor conditions.

ABSTRACT

LiFi (light-fidelity) is recognised as a promising technology for the next generation wireless access network. However, little research effort has been spent on the uplink transmission system in LiFi networks. In this paper, an analytical framework for the performance analysis of an wireless infrared-based LiFi uplink at system level is presented. This work focuses on the performance of a single user who is randomly located in a network. Many important factors in practice are taken into account, such as front-end characteristics, channel path loss, link blockage and user device random orientations. In particular, accurate analytical expressions for the statistics of optical channel path loss has been derived. Based on this path loss statistics, the distribution of signal-to-noise ratio (SNR) and the average achievable data rate are evaluated. A channel factor is defined as a quantity which only depends on the used devices, optical channel and noise power spectral density function (PSD). The result shows that with commercial front-end elements, an average data rate of up to 250 Mbps is achievable.

Motivation & Objective

• To address the lack of systematic performance analysis for uplink transmission in LiFi networks, particularly focusing on wireless infrared-based uplink.
• To model and quantify the impact of practical impairments such as random user equipment (UE) location, orientation, and human body blockage on uplink channel quality.
• To develop an accurate analytical framework for optical channel path loss statistics in a realistic indoor LiFi environment.
• To evaluate the resulting signal-to-noise ratio (SNR) distribution and average achievable data rate under these practical constraints.
• To define and analyze a channel factor that encapsulates device-specific and environmental parameters, enabling performance prediction independent of specific channel realizations.

Proposed method

• Derives analytical expressions for the statistics of optical channel path loss by modeling the line-of-sight (LoS) component based on user equipment position and orientation using spherical coordinates and cosine-based gain functions.
• Incorporates the effects of link blockage by human users (NUBs) through a probabilistic blockage model, assuming independent blockage events with a blockage probability $\bar{\mathcal{P}}_{\rm b}$.
• Uses a truncated Laplace distribution to model the angular deviation of the user equipment's orientation, enabling tractable integration over random orientations.
• Applies asymptotic approximation techniques to evaluate the cumulative distribution function (CDF) of the channel gain $G$, using a piecewise function $\mathcal{Y}_0(T)$ to balance accuracy and computational complexity.
• Introduces a channel factor that depends only on front-end device characteristics, optical channel parameters, and noise PSD, enabling performance evaluation independent of instantaneous channel state.
• Employs numerical integration and special functions (exponential integral $\mathrm{Ei}$, Q-function, Dirac delta) to compute the CDF of the channel gain and SNR distribution.

Experimental results

Research questions

• RQ1 How does the statistical distribution of optical path loss vary with random user equipment location and orientation in a LiFi uplink system?
• RQ2 What is the impact of human body blockage on the reliability and data rate of an infrared-based LiFi uplink?
• RQ3 How can the signal-to-noise ratio (SNR) distribution be analytically modeled under realistic channel uncertainties?
• RQ4 What is the achievable average data rate in a wireless infrared LiFi uplink when accounting for path loss, blockage, and device characteristics?
• RQ5 How can a channel factor be defined to encapsulate system-specific parameters and enable scalable performance evaluation?

Key findings

• The paper derives an accurate analytical expression for the cumulative distribution function (CDF) of the optical channel gain, incorporating path loss, user location, orientation, and blockage effects.
• The SNR distribution is shown to be highly dependent on the user’s random position and orientation, with significant variation across the room, especially near blockage zones.
• The average achievable data rate in the system is analytically evaluated and shown to reach up to 250 Mbps when using commercial front-end components and under realistic deployment conditions.
• The channel factor is defined as a system-level metric that depends only on device characteristics, optical channel parameters, and noise PSD, enabling performance prediction without full channel state knowledge.
• The proposed approximation method for the CDF of the channel gain achieves high accuracy (error threshold $1 \times 10^{-2}$) across the dynamic range of interest, validated through numerical integration.
• The model accounts for the non-uniformity of signal strength due to user mobility and blockage, demonstrating that blockage probability significantly degrades average data rate unless mitigated by beamforming or diversity.