Hello gurpreet
Most of the answers of your question already been given by Alisthu about sac ocdma and how to consider there parameters.I just want to add about FSO distance you acheived.You can enhance the transmission distance more ,but it strongly depends upon what values of fso parameters you are taking.beam divergence,scintillation,attenuation are some of the important factors to be considered.i would also suggest you to study effects if different atmospheric turbulences on your system by taking the effects of fog,light fog,heavy fog,haze and clear weather.you just need to set the values of attenuation to realize these turbulences on system