Experimental of realtime transmitter PAM-4 for optical wireless communication systems

This paper presents a realtime experimental demonstration of multi-level pulse amplitude modulation (MPAM) for optical wireless communication systems. The PAM of 4-levels with the sampling rate of the digital-to-analog (DAC) of 100 MHz is studied. As a result, the bit rate of 200 Mbps can be achieved. The PAM-4 signal is generated by using a field-programmable gate array (FPGA) in realtime with the pseudo random bit sequence of 7 (PRBS-7). At the transmitter, a laser diode with lambda of 405 nm is used. A bias-T which is used to drive the laser is self-developed and implemented in our laboratory. There are two scenario tests; one is short distance with long system running and the second is long distance of communication systems. The results show that the received signal is very clear to understand when compared with the transmitted signal. The system still works very well after letting the system running for 13 hours.