Far-field approximate expressions for average irradiance and average BER in flat-topped beam-based optical wireless communication links under pointing error and gamma–gamma turbulence

The flat-topped beam possesses a unique characteristic of reduced beam spreading in atmospheric turbulence, which can enhance the signal-to-noise ratio of atmospheric optical wireless communication (OWC). However, due to the complexity of the irradiance expression for flat-topped beams, the average bit error rate (BER) of flat-topped beam-based OWC links has rarely been theoretically derived in previous studies. In this work, we propose, for the first time, to our knowledge, a far-field approximate expression for the average irradiance of flat-topped beams. Based on this, a novel far-field approximate expression, to our knowledge, for the average BER of flat-topped beam-based OWC is deduced under the combined effects of pointing errors and gamma-gamma turbulence. Furthermore, the far-field approximate criterion for average irradiance is investigated via simulations. And then, the application ranges of the far-field approximate expressions for average BER can also be determined. This work proposes a far-field approximate approach for the rapid analysis and design of flat-topped beam-based OWC links under pointing errors and gamma-gamma turbulence. For future research directions, the proposed approximate approach could be extended to investigate high-order Gaussian beam-based OWC links under various turbulence and pointing error conditions.