Problem
Research questions and friction points this paper is trying to address.
LiFi
Link-budget
Receiver constraints
Noise budget
Eye safety
Diffused-Beam Laser-Diode LiFi Under Realizable Receiver, Noise, and Safety Constraints: Design-Space Analysis and an Open Cross-Verified Simulation Framework
🤖 AI Summary
This study addresses the overestimated performance in existing LiFi link budgets caused by idealized assumptions by proposing a design space analysis framework for diffuse laser LiFi constrained by hardware feasibility. By coupling a holographic diffusion channel model with a comprehensive receiver noise budget incorporating laser RIN, this work evaluates PAM modulation, multipath effects, and eye safety constraints. Furthermore, an open-source ns-3 simulation module validated by prototyping is released. Experimental results demonstrate a data rate of 558 Mb/s at 5 meters, revealing that idealized models overestimate performance by 3.9 to 6.6 times. These findings confirm the effectiveness of the proposed framework in correcting prediction biases and guiding practical system design for realistic diffuse laser LiFi deployments.
📝 Abstract
Link-budget studies of indoor optical wireless systems frequently assume receiver parameter sets--large photodetector area, large transimpedance, and wide bandwidth simultaneously--that violate basic circuit constraints, and noise budgets that omit dominant amplifier and laser noise. This paper develops a realizability-constrained design-space analysis of a diffused-beam laser-diode (LD) LiFi link anchored to a hardware prototype. The analysis couples the generalized Lambertian channel of a holographic-diffuser source to a receiver model that enforces the transimpedance-amplifier gain-bandwidth/capacitance constraint and carries a complete noise budget: shot, feedback-resistor thermal, input current noise, capacitance-driven voltage-noise gain, and laser relative intensity noise (RIN). Against this budget we evaluate unipolar M-PAM under two FEC tiers (7%-overhead hard-decision at $3.8 \times 10^{-3}$, 20%-overhead soft-decision at $2 \times 10^{-2}$), first-bounce diffuse multipath, and a quantitative extended-source eye-safety assessment. The full model predicts 140 Mb/s net at the prototype's demonstrated 14-m range with 6.7 dB margin (OOK, HD tier), 240 Mb/s at the zero-margin 4-PAM/SD reach boundary of 14.0 m, and 480-558 Mb/s at 5 m--a factor 3.9-6.6 below what the same link yields under a naive textbook budget, quantifying how strongly idealized assumptions inflate LiFi projections. First-bounce analysis shows the downfacing-source/up-facing-receiver geometry confines multipath to a worst-case LOS-to-diffuse ratio of 4.2 dB and delay spreads below 0.13 ns, and the 500-mW source remains a factor $\ge 7.8$ under the Class-1 eye-safety limit. All models are released as an ns-3 module and Python engine backed by automated testing.
Innovation
Methods, ideas, or system contributions that make the work stand out.
Realizability-constrained design-space analysis
Complete noise budget
Diffused-beam laser-diode LiFi
Eye-safety assessment
Open cross-verified simulation framework
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