Tightened Upper Bounds for Coded FSO Links over Atmospheric Turbulence Channels

The upper bound of error rate performance of coded free space optical (FSO) communication system is studied in this paper. A new tightened upper bound over fully interleaved turbulence channel is proposed based on Gallager´s second-bounding techniques. Two turbulence models are considered, log-normal model for weak fluctuation scenarios and negative exponential model for strong fluctuation scenarios. To simplify the computation complexity, the derived bound, the second version of the Duman-Salehi (DS2) exponential bound, is derived into closed-form expression by selecting an optimal tilting measure. Meanwhile, for comparison, the union bound is also discussed starting with the approximation of pairwise error probability. Furthermore, we present the analytical approach for average weight enumerator of turbo product codes. Then the DS2-exponential bound along with union bound are applied for these codes, of which performance bounds are seldom discussed in the literature. Simulation results are also presented to shed light on the tightness of our derived bounds.