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Interleaved superposed-64QAM-constellation design for spatial multiplexing visible light communication systems.

Xinyue Guo, Yuansha Yuan, Chao Pan

|October 7, 2021

Summary

A new superposed 64-quadrature amplitude modulation (QAM) constellation improves visible light communication (VLC) systems using 2x2 multiple-input multiple-output (MIMO). This novel scheme reduces nonlinear distortion and enhances bit error rate (BER) performance.

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Area of Science:

Optoelectronics
Wireless Communication

Background:

Visible Light Communication (VLC) systems increasingly use superposed constellations and spatial multiplexing Multiple-Input Multiple-Output (MIMO) for multiplexing gains.
Channel correlation does not limit the effectiveness of these techniques in VLC.

Purpose of the Study:

To propose a novel superposed 64-quadrature amplitude modulation (QAM) constellation scheme for 2x2 MIMO VLC systems.
To address light-emitting diode (LED) nonlinearity by introducing geometrically shaped 8QAM constellations to reduce the peak-to-average power ratio (PAPR).

Main Methods:

Developed a superposed 64QAM constellation by interleaving two geometrically shaped 8QAM constellations.
Ensured a power ratio of 1 between transmitted signals to minimize nonlinear distortion and signal-to-noise ratio (SNR) deterioration.
Experimentally evaluated system performance under varying transmitted powers, direct current bias currents, and driving peak-to-peak voltages (Vpps).

Main Results:

The proposed superposed 64QAM scheme demonstrated superior bit error rate (BER) performance compared to traditional schemes.
Achieved an improved dynamic range for driving Vpps (0.06 to 0.4 V and 0.23 to 0.4 V) below the 7% pre-forward error correction BER threshold (3.8 × 10⁻³).
Minimized nonlinear distortion and avoided SNR deterioration due to power competition.

Conclusions:

The novel superposed 64QAM constellation effectively enhances performance in 2x2 MIMO VLC systems.
The use of geometrically shaped 8QAM constellations mitigates LED nonlinearity and improves system robustness.
The proposed scheme offers significant advantages in terms of BER and operational dynamic range.