Statistical model for the weak turbulence-induced attenuation and crosstalk in free space communication systems with orbital angular momentum.

A novel statistical model connected with turbulence strength is proposed to describe the attenuation and crosstalk in a vortex-based multi-channel free space optical (FSO) communication system. In this model, self-channel fading and interference between different orbital angular momentum (OAM) modes are characterized by the mixture exponential-generalized-gamma (EGG) distribution, and the analytical relations between turbulence strength and the distribution function's parameters are expressed by piecewise functions. The problems of obtaining parameters of this model are converted into optimization problems, and the algorithms based on the trust trigon algorithm are proposed to achieve more optimized parameters. This model is confirmed to have a good fit with the emulated data of OAM attenuation and crosstalk calculated by the square of the scalar product between the fields of two OAM modes. Furthermore, the application of the statistical model to the OAM-multiplexing FSO system with quadrature-phase-shift-keying modulation is presented, in which the theoretical average bit-error rate results match well with Monte Carlo simulation. This model can be used for FSO system design with OAM for continuous weak turbulence condition.