Researchers present a new comprehensive framework for modeling pointing error in quantum key distribution optical wireless systems
Quantum key distribution (QKD) is an emerging communication technology that utilizes quantum mechanics principles, enabling the sender and receiver to generate a shared secret key over a channel that may be monitored by an attacker. Among the various parameters that influence the performance of QKD systems, pointing error, a misalignment between the transmitter and receiver, is one of the most important. Despite its importance, very few studies have examined pointing error in a comprehensive manner for QKD optical wireless communication (OWC) systems.
To address this gap, a new study published in Volume 61, Issue 6 of the IEEE Journal of Quantum Electronics on December 1, 2025, presented a comprehensive analytical framework for modeling the effect of pointing error on QKD OWC system performance. “By combining statistical models of beam misalignment with quantum photon detection theory, we derived analytical expressions for key performance indicators of QKD systems, clarifying the exact role of pointing error in degrading secure key generation,” explains Professor Yalçın Ata from OSTIM Technical University, Turkey.
The researchers focused on widely used BB84 QKD protocol and modelled pointing errors using Rayleigh and Hoyt distributions. Using these statistical models, they first derived analytical expressions for error and sift probabilities under pointing error, a first in the field. These were then used to compute the quantum bit error rate (QBER) and calculate the secret key rate (SKR). They analysed the effects of pointing error caused due to both symmetric and asymmetric beam alignments.
The results showed that an increased beam waist, and hence, increased pointing error, significantly degrades QKD performance, indicated by higher QBER and decreased SKR. Increasing receiver aperture size can improve performance, but only up to a certain level. Interestingly, asymmetric beam misalignment, where horizontal and vertical deviations are different, was found to be favourable for improving performance.
“Our findings, based on Rayleigh and Hoyt framework, are consistent with existing generalized models, while offering new analytical clarity on the role of asymmetry in pointing errors,” concludes Prof. Ata.
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