Fortifying the Backbone: Shielding HAPS Backhaul From Intelligent Jamming

Abstract

High altitude platform stations (HAPS) as International Mobile Telecommunications (IMT) base stations (BSs) or HIBS have emerged as a key enabler to extend wireless connectivity to remote areas, emergency services coordination, and backhaul support. However, security remains a critical concern in such deployments due to the broadcast nature of the shared medium, which introduces various privacy and security vulnerabilities such as eavesdropping and jamming attacks. This paper addresses an active attack, in other words, jamming on the backhaul link in the HIBS network, which has been overlooked in favor of access link security analysis. We propose a potential threat model for access and backhaul links with an intelligent behavior, i.e., an adaptive access/backhaul jammer that leverages antenna radiation pattern knowledge for strategic positioning. The results show that intelligent jamming can cause the signal-to-jamming-plus-noise ratio (SJNR) in access to drop to -4 dB, while backhaul link SJNR degrades to -30 dB in worst-case scenarios. Additionally, the access and backhaul links experience a throughput loss of up to 50% and 89%, respectively. Our comparison analysis demonstrates that a single attacker compromising the backhaul link causes a more significant degradation in HIBS network than an attacker targeting multiple access links. Therefore, shifting the focus to addressing the backhaul jamming, we adopt the Direct Sequence Spread Spectrum (DSSS) technique as a countermeasure in a directional setup with perfect alignment, which shows effective mitigation of jamming interference with a SJNR improvement of 30 dB and throughput improvement of 56%, inside the vulnerability zone. In the context of this study, the vulnerability zone is the region where the adaptive access/backhaul jammer is autonomously positioned to cause maximum interference in access or backhaul. Moreover, the proposed DSSS approach with perfect directional antenna alignment and misalignment case is compared with the baseline DSSS in omnidirectional antenna setups. The results demonstrate the superiority of the proposed DSSS over the baseline scheme even under antenna misalignment in the backhaul link.