The Investigation For Atomospheric Effect Reduction In Optical Wireless Communication

Optical wireless communication (OWC) conveys signal by optical beampropagating through the atmosphere. This kind of commucation can obtain a great dealof transmission capacity in a very flexible way and with much lower cost than thecommunication system we are using now. However, the atomosphere channel is randomand heterogeneous, its influence on optical beam will seriously degrade the performanceof OWC system. People have studied some techniques to improve the reliability ofOWC system, such as modulation technique、 amplification、 diversity and relaytechnology ect, and now these technologies are being applied to OWC system gradually.My team have designed a set of wireless optical communication systemindependently, for better performance, it’s necessary to investigated those atomosphericeffect reduction technologies.Firstly, wireless optical communication system based on circular polarization shiftkeying (CPolSK) modulation is studied. The principle of CPolSK modulation system isintroduced, the performance of systems based on PolSK modulation and severalcommon intensity modulation are analized. And the result of simulation reseach on theCPolSK system and OOK system show that, CPolSK system perform much better onthe eye diagram、BER and sensitivity compared with OOK system, the BER of CPolSKis four order of magnitude lower and the sensitivity is higher, which accord with therelevant experiment validate.Next, simulation reseach on two OWC systems with optical amplification is carriedon, one system model has an optical amplifier at the transmitter and the other at thereceiver. The simulation results show that the effective transmission distance、linkredundancy and BER performance all have greatly promoted for the system with opticalamplification at the transmitter than the system with optical amplification at the receiver.What’s more, the system with an amplifier at the transmitter shows much better eyediagram and a higher SNR value in the same condition, which results in theperformance difference of the two systems.At last, a spatial diversity reception method based on telescope array is put forward,and combined with adaptive control on the optical signal amplitude and phase, a furthertelescope array receiving method based on adaptive control technology is proposed. Andby simulation, it indicate that the receiving method can increase the receiving sensitivity,decrease the BER, and improves system performance greatly.