Bandwidth Enhancement in White LED Visible Light Communication Systems Using Blue Optical Filtering and Multi-Stage Equalization
Visible Light Communication (VLC) enables short-range high-speed data transmission using
white light-emitting diodes (LEDs) for both illumination and communication. However,
phosphor-converted white LEDs suffer from limited modulation bandwidth due to slow
phosphor relaxation dynamics, resulting in signal attenuation, inter-symbol interference (ISI),
and degradation of signal-to-noise ratio (SNR) at higher frequencies. In this work, performance
enhancement using blue optical filtering combined with electrical equalization was
experimentally investigated for phosphor-converted white LEDs transmitting On-Off Keying
Non-Return-to-Zero (OOK-NRZ) signals. Measurements were conducted over a 40 cm indoor
line-of-sight link with data rates varied from 0.5 to 20 Mbps. Two equalizer configurations
were evaluated: a single-stage RC network (EQ1) and a three-stage cascaded RC network
(EQ2). Frequency sweep measurements (representing OOK symbol rate variation) were
performed to evaluate received signal strength, SNR, Bit Error Rate (BER), cumulative signal
improvement, and normalized performance metrics. Results show that EQ2 provides
significantly superior performance compared to EQ1, achieving a peak SNR of 34 dB at 10
Mbps with a corresponding BER reduction to 10??, representing approximately 8 dB SNR
improvement over EQ1 at the optimal frequency. The optimal enhancement region for EQ2 lies
between 0.5 and 12 MHz, where LED channel attenuation is most dominant. Polynomial fitting
was used as an empirical approximation, with fifth-order models providing the highest
regression accuracy for EQ2 (R² = 0.90). The results demonstrate that the combination of blue
optical filtering and multi-stage equalization effectively mitigates LED bandwidth limitations,
significantly improving VLC performance for indoor smart lighting and short-range wireless
applications.