Comparison of different modulation techniques for free space laser communication

Free Space Optical (FSO) communication is the system of transmission of data using a wireless medium, which uses modulated near infrared light beams as carrier wave. Free-space optical communication has gained a lot of popularity as an alternative to radio frequency (RF) communication over the last two decades. Most of the time Optical communication has the edge over baseband or RF transmission systems whenever it is involved with high aggregate bit rates and/ or very long transmission distances. This paper intends to give an overview of Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM) and Frequency Shift Keying (FSK) modulation techniques and compares their characteristics over a diode laser in free space using a carrier signal having a frequency no more than 5 KHz.