In areas such as disaster sites, offshore platforms, and above river surfaces, there are signal blind spots for cellular networks. When low-altitude aircraft operate, they may not be able to connect to the system and communicate with the control center. Existing methods achieve network coverage by deploying dedicated cellular base stations on the ground or installing satellite communication modules on the aircraft, but these methods are expensive. A multi-network fusion Unmanned Aerial Vehicle (UAV) network-assisted access system has been designed and implemented. This system consists of gateway UAVs, relay UAVs, and UAVs providing access services. The UAVs are connected through ad hoc networks, and data is relayed from the UAV providing access services to the gateway UAV via the relay UAVs and multi-hop transmission. The system uses commercial low-cost embedded devices and ad hoc network modules to achieve functions such as automatic network configuration, seamless roaming, and session persistence. In prototype system experiments, UAV nodes can complete self-organization deployment within 3 s and achieve roaming switching within 0.65 s, with an uplink throughput of 11.15 Mbps and a downlink throughput of 15.98 Mbps. Under dynamically changing low-altitude topologies, the system completes routing convergence within 1.5 s, significantly outperforming the OLSR routing protocol about 4.15 s. The effective communication distance is extended to nearly 1 km, and the per-node total power consumption remains below 100 W, which is considerably lower than existing UAV-based communication solutions. The system performs well in terms of coverage, connection stability, and business continuity, providing reliable network access services for low-altitude communication blind areas at a low cost.

We consider the extrema estimation problem in large-scale radio-frequency identification (RFID) systems, where there are thousands of tags and each tag contains a finite value. The objective is to design an extrema estimation protocol with the minimum execution time. Because the standard binary search protocol wastes much time due to interframe overhead, we propose a parameterized protocol and treat the number of slots in a frame as an unknown parameter. We formulate the problem and show how to find the best parameter to minimize the worst-case execution time. Finally, we propose two rules to further reduce the execution time. The first is to find and remove redundant frames. The second is to concatenate a frame from minimum value estimation with a frame from maximum value estimation to reduce the total number of frames. Simulations show that, in a typical scenario, the proposed protocol reduces execution time by 79% compared with the standard binary search protocol.