A Highly Reliable FSO/RF Communication System Using Efficient Codes

Optical wireless systems can solve many of the long standing problems of providing low-cost time-constrained high- bandwidth communication in a variety of network scenarios. But their unreliability due to variations in atmospheric channel make them the least deployed solutions so far. Achieving enterprise level reliabilities in such scenarios is difficult. Earlier solutions make use of a backup RF channel which transmits data whenever the FSO link is down. However, only one channel is operational at a time wasting the bandwidth of the other channel. Also this system faces the problem of alternate switching between both the channels in case the channel conditions vary from good to bad. In this paper, we propose a novel coding paradigm called "Hybrid Channel Coding" that not only optimally achieves the capacity of the combined FSO and RF channels but still provides carrier grade (99.999%) reliabilities for the FSO link. We provide the design methodology to be used in constructing Hybrid Channel Codes. Using analysis and simulation, we show that we can obtain many-fold decrease in the channel availability and maximum throughput with Hybrid Channel Codes.