Pulse-number modulation method for free-space optical communication based on FPGA

In Free-Space Optical (FSO) communication, with the increase of bit resolution of M, the required bandwidth of PPM and DPIM increase sharply, and the bandwidth efficiency are extremely low. There is also a clock synchronization problem in the demodulation process of PPM and OOK. We propose a pulsed-laser Pulse-Number Modulation (PNM) method to address the high required bandwidth and low bandwidth efficiency for high-order modulation in FSO communication with traditional modulation methods. The symbol structure, power efficiency and bandwidth properties of PNM are presented. The modulation and demodulation of PNM are simple and easy to implement without complex clock synchronization processing. Additionally, we use the FPGA as the core controller to build an FSO communication system, which realizes accurate modulation and demodulation of data with PNM modulation method under the communication distance of 27 m and the bit rate of 2.5K bps.