Low-latency mac-layer handoff for a high-altitude platform delivering broadband communications

Abstract

This paper presents a low-latency handoff algorithm that exploits the unique characteristics of a high-altitude platform (HAP) multi-cell system payload to significantly reduce the need for payload stabilization. The handoff algorithm incorporates a novel time reuse Time-Division Multiplex/Time-Division Multiple Access (TDM/TDMA) frame structure, similar to that available with IEEE 802.16. Single-and multiple-frequency variants have been developed, with the intention of keeping the handoff process transparent to the user. The multiple-frequency variant is designed to increase system capacity by using a sequence of frequencies in different parts of the frame. Performance of the single-frequency-band handoff scheme is assessed using a generic pitch model. It has been shown to perform robustly, offering low-latency handoff, even with very short cell dwell times. Using a number of developed HAP mobility models — such as bounce, random walk, and rotation — the worst-case handoff performance is also quantified for a distribution of fixed users within a coverage area. It is shown that local user traffic hotspots are the dominant factor affecting performance, but that mitigation strategies are available.