Research on Modulation Properties of Atmospheric Wireless Optical Communication

Currently, the atmospheric wireless optical communication generally uses intensity modulation/direct detection (IM/DD) systems. There are typical modulation schemes such as on-off keying (OOK), pulse position modulation (PPM), differential pulse position modulation (DPPM), differential pulse interval modulation (DPIM) and dualheader-pulse interval modulation (DH-PIM) for atmospheric wireless optical communications. For the high packet error rate and low information transmission rate of wireless optical communication intensity modulations presently, which is caused by atmospheric turbulence and scintillation on the laser beam, a new modulation scheme--Polarization Shift Keying is proposed. The modulation structures, bandwidth requirement, transmission capacity, power requirement and packet error rate performance over weak turbulence are compared between several intensity modulation schemes (including OOK, DPPM, DPIM, DH-PIM) and PolSK modulation. Theoretical analysis and simulation results show that OOK offers the highest bandwidth efficiency and transmission capacity. However, the average transmission power and bit error rate is both high. The reliability of DPPM and DH-PIM is better, while the bandwidth efficiency is low. CPolSK offers the highest bandwidth efficiency and the lowest bit error rate and packet error rate, which are very important in the atmospheric wireless optical communication. CPolSK has stronger anti-interference ability compared to intensity modulation scheme, because the polarization seems to be the most stable characteristic of a laser beam while propagating through the atmosphere. Hence, CPolSK is superior in the atmospheric laser communication.