Research On Automatic Switching Of Hybrid FSO/RF System Based On Atmospheric Channel

The basic theories, state-of-the-art and development of free space optical (FSO) and radio frequency (RF) communication are introduced in this paper. In order to ensure the transmission quality of FSO, a hybrid FSO/RF system used to decrease the attenuation of FSO transmission signals is presented for the problem of decreasing reliability owing to the severe environment of the atmospheric channel. Then the automatic switchover performance of the two links of the system is analyzed and researched, and the results show that the availability of the hybrid system is better than the single link.According to the newest recommendation of ITU-R, the effects on signal transmission caused by atmospheric attenuation and turbulence are deeply analyzed, especially clouds, fog and rain scattering. The physical and mathematical model of hybrid FSO/RF system is designed, the flow chart of FSO communication is provided and the link performance is simulated. The physics meaning of the flow chart is clear, and its format is simple. Moreover, by performance simulation of the atmospheric attenuation channel and the turbulence channel, the differences between light spots of two channels are simulated and an important conclusion is concluded that the received power is suitable for describing the atmospheric attenuation channel while the received light spots are suitable for describing the atmospheric turbulence channel.Based on the performance analysis of the received power and bit error rate (BER), two certain thresholds for link switchover are deduced and a new switchover scheme is put forward. Digital signal processor (DSP) is used for judgment and a matrix on-off is used for implementing switchover. In addition, by comparing the simulation performance with the former experimental results of hybrid FSO/RF system, the results show that they are similar with each other.