Power Efficiency Analysis of Spatial Diversity Based Vertical FSO Links With Pointing Error in Multiple Beam Transmissions

Abstract

In this paper, we analyzed the diversity performance with increased pointing error caused by multiple beam transmissions for spatial diversity based vertical free space optical (FSO) back-haul links. For power-limited FSO systems, the spatial diversity technique can be employed to mitigate the atmospheric fading issues in vertical FSO links. However, the arrangement of multiple transmitters to achieve independent channels can cause additional alignment errors in the misalignment detection process of pointing, acquisition, and tracking (PAT) systems, as demonstrated by the experiment results. The increase of misalignment makes the pointing loss severe to reduce the achievable diversity gain, which results in insufficient received power to satisfy the system requirements. The system optimization with the statistical misalignment model can mitigate the effect of increased pointing error and improve the diversity gain as the number of channels increases. The proposed scheme provides an enhanced link margin for designing seamless FSO wireless back-haul networks for next-generation wireless communication systems.

Bidirectional Atmospheric Channel Reciprocity-Based Adaptive Power Transmission

“…where f (r) is the probability density function (PDF) that obeys a normal distribution under turbulent conditions, Q(•) denotes the Gaussian function, N C denotes the noise present in the channel, and N PD denotes the noise generated by the photodetector in Equation (7). In summary, the adaptive power technique proposed in this paper can effectively mitigate the effects of noise in bidirectional atmospheric channels.…”

“…Researchers have investigated a variety of effective communication techniques to deal with the adverse impacts brought on by atmospheric turbulence. Multibeam light was proposed to be used for information transmission in FSO links in the literature [7,8], However, multibeam means multichannel, and the pointing inaccuracy is not insignificant. Multimode aperture diversity reception was studied in the literature [9,10] to minimize turbulence damage.…”