Diversity Based on Oversampling Technique for PAM-4 in Optical Wireless Communication Systems

This paper utilizes the concept of oversampling to achieve diversity for optical wireless communication (OWC) systems with four levels pulse amplitude modulation (4-PAM). We propose two contributions to the development of OWC applications. The first one is the implementation of realtime PAM-4 transmitter (Tx) using field-programmable gate array (FPGA). The second one is diversity using oversampling method which can be used to improve the system performance. In this case, each symbol is sampled more than two times, and, averages them all together.  The proposed method is fully verified by experimental demonstration for both Tx realtime implementation and the receiver (Rx). The digital PAM format from FPGA is converted to analog format by using a digital-to-analog converter (DAC). With the update rate of 400 Msps, the proposed OWC systems can provide the communication speed over 800 Mbps; and, only a few FPGA resource usages are consumed. The experimental results showed that the bit error rate (BER) free can be achieved applying diversity using oversampling with four taps. Additionally, the communication distances up to 14 m is successfully transmitted