Altitude Layer Network PLET & PRET in AAM Corridors
How predicted link and route expiration times change when drones are
organized into altitude lanes — and why cross-layer links are the
weakest point in trajectory-aware routing.
Saumya Gupta · Trajectory-Aware Route Maintenance for Drones in AAM MANETs
PLET
Predicted Link Expiration Time — how long two nodes will remain within transmission range, computed from future trajectories.
PRET
Predicted Route Expiration Time — the minimum PLET along a multi-hop route. The weakest link determines route lifetime.
UTM altitude lanes
Real AAM design separates drones into altitude layers by direction of travel, creating a layered network topology problem.
Drones in the same altitude layer travel in the same direction.
Relative velocity between neighbors is low, so they stay within
transmission range for many future timesteps.
PLET is high — these are stable, long-lived links a routing
protocol should prefer.
Cross-layer links — low PLET
Cross-layer links connect drones on opposite-direction lanes.
They converge, briefly enter range, then diverge rapidly.
Even when R is large enough to form the link, PLET is low —
the link dissolves quickly. A PRET-aware protocol avoids routing
through these hops.
Key observation
Drag R slowly upward past the layer gap. You will see the network "connect vertically" —
cross-layer links appear for the first time. But notice that the
PLET labels on cross-layer links are consistently lower than same-layer ones,
even at the same horizontal distance. This is the altitude-layer topology problem:
PRET on any route through a cross-layer hop is bounded by that hop's low PLET,
regardless of how stable the same-layer segments are.
This creates a natural stratification in routing quality that PLET/PRET-aware protocols
can exploit — and that conventional hop-count routing cannot see at all.