Average capacity of the ground to train communication link of a curved track in the turbulence of gamma-gamma distribution

- Effects of curved tracks on optical wireless communication links of ground-to-train are studied.
- A model of the average capacity for communication links of the ground to train is developed.
- Heavier fog reduces the average capacity of links in gamma-gamma distribution turbulence.
- Pointing errors and average signal-to-noise ratio of free space links reduce link performance.
- The impact of the non-Kolmogorov spectral index on the average capacity can be ignored.

A model of the average capacity of optical wireless communication link with pointing errors for the ground-to-train of the curved track is established based on the non-Kolmogorov. By adopting the gamma-gamma distribution model, we derive the average capacity expression for this channel. The numerical analysis reveals that heavier fog reduces the average capacity of link. The strength of atmospheric turbulence, the variance of pointing errors, and the covered track length need to be reduced for the larger average capacity of link. The normalized beamwidth and the average signal-to-noise ratio (SNR) of the turbulence-free link need to be increased. We can increase the transmit aperture to expand the beamwidth and enhance the signal intensity, thereby decreasing the impact of the beam wander accordingly. As the system adopting the automatic tracking of beam at the receiver positioned on the roof of the train, for eliminating the pointing errors caused by beam wander and train vibration, the equivalent average capacity of the channel will achieve a maximum value. The impact of the non-Kolmogorov spectral index's variation on the average capacity of link can be ignored.