Grouped modulation scheme for led array module in a visible light communication system

Grouped modulation is proposed to generate multiple-level optical signals and enhance the data rate for LED-array-module-based indoor visible light communication systems. By dividing LEDs in an array module into n groups and driving different groups with separate circuits, 2nlevel modulation can be realized with binary modulation for each group. The maximum driven current for respective circuits is reduced compared to that of the same multiple-level PAM for which an array module is driven by a single circuit. The limitation to modulation bandwidth of an LED array module, caused by the product of gain and bandwidth of its driven circuit, is alleviated. The benefit of grouped modulation is that the performance of a visible light communication system can be improved with the medium complexity of driven circuits for different groups. Proof-of-concept experiments demonstrate that the data rate can be enhanced up to 50 Mb/s with three LEDs (LED465E provided by THORLABs) by 2-grouped OOK modulation and the transmission length is 1.0 m with a bit error rate less than 1e-6. Meanwhile, the maximum current of driven circuits for two groups is reduced by a third compared to a circuit driving three LEDs as a whole. The improvements can be further increased greatly if a larger-sized LED array module of hundreds or thousands of LEDs is divided into more groups. Grouped modulation can also be extended to other formats such as pulse position modulation and overlapping pulse position modulation.