Functional Symmetry in Shared-Pool UAV Service Architectures for Wireless Sensor Network Availability

This paper proposes and analyzes a symmetry-based shared-pool architecture for service continuity in UAV-assisted wireless sensor networks with aerial base station placement. Unlike the conventional dedicated architecture, in which individual sensor clusters are structurally associated with specific serving UAVs and replacement units provide cluster-centered redundancy, the proposed architecture treats all available UAVs as a common pool of functionally interchangeable service units that can be dynamically assigned to active clusters. The novelty of the approach lies in formalizing this functional interchangeability as permutation symmetry of the underlying stochastic model. Under homogeneous UAV reliability parameters and homogeneous cluster-demand characteristics, relabeling UAVs or non-tagged clusters does not change the system dynamics. This invariance permits the identity-dependent microscopic state space to be reduced to occupation-number macrostates defined by the number of unavailable UAVs and simultaneously active service demands, while symmetric access in overloaded states determines the tagged-cluster service probability. On this basis, an analytical availability model is developed that combines UAV failure–recovery dynamics, limited recovery capacity, stochastic cluster activity, and demand-driven allocation from a shared aerial resource. The proposed architecture is compared with a dedicated-service baseline under both equal-fleet and target-availability criteria. The results show that shared pooling can convert permutation-based functional symmetry into a practical fleet-efficiency gain: under low or moderate demand overlap and adequate recovery capacity, the same service-continuity target can be achieved with fewer UAVs than in the dedicated architecture, whereas the advantage decreases under strong demand overlap or severe pool depletion. The study therefore establishes a direct link between permutation symmetry, stochastic state-space reduction, shared redundancy, and UAV fleet efficiency in service-oriented aerial sensor networks.