## 1 Introduction  
Over the last 15 years, Wireless Sensor Networks (WSNs) have been studied extensively and applied in a large number of real world applications, ranging from environment monitoring (e.g., pollution, agriculture, volcanoes, structures and buildings health), to event detection (e.g., intrusions, fire and flood emergencies) and target tracking (e.g., surveillance). WSNs usually generate a large amount of data by sensing their environment and detecting events, that must be managed and forwarded to a Sink node in an efficient and reliable manner. The introduction of mobility in WSN has attracted significant interest in recent years [1]. Mobility can be introduced in any component of a sensor network, including the regular sensor nodes, relay nodes (if any), data collectors, sink or any combination of these. From nodes deployment and localization to data routing and dissemination, mobility plays a key role in almost every operation of sensor networks. For instance, a mobile node can visit other nodes in the network and collect data directly through single-hop transmissions [2]. Similarly, a mobile node can move around the sensor network and collect messages from sensors, buffer them, and then transfer them to the Sink [3]. This significantly reduces not only message collisions and losses, but also minimizes the burden of data forwarding by nodes, and as a result spreads the energy consumption more uniformly throughout the network [1]. Mobility can also improve WSNs in terms of extending lifetime [4], coverage [5], reliability [6], and channel capacity [7]. A detailed survey on the usage and advantages of mobility in different phases of the WSN operation is given in [8]. Unmanned Aerial Vehicles (UAVs) are increasingly being used in WSNs, due to the cost-effective wireless communication and surveillance capabilities they provide [9]. UAVs play a prominent role in a variety of real world applications like homeland defense and security, natural disaster recovery, real-time surveillance, among others. UAVs and WSNs can cooperate in a number of different ways to improve network efficiency and performance [10; 11; 12; 13; 14]. Benefits can be identified in both directions. For instance, UAVs that have more resources for sensing and computing, can move to particular locations to perform more complicated missions. In addition, the WSN could provide extended sensory capabilities to guide the navigation of UAVs. In order to support simultaneous interaction with WSN and Sink, the UAV must have at least two types of communication protocols. As sensor nodes have constrained resources, their communications protocol should be efficient and have a small footprint. This holds for communication among the WSN nodes as well as WSN-to-UAV and UAV-to-WSN. When considering communication between the UAV and the Sink, more robust protocols can be adopted, given that both sides have much more computing power when compared to the nodes in a WSN. In order to support UAV-to-Sink communication, there are two possibilities: either the UAV carries a second radio (with different physical layer) or it uses the same radio for both purposes. Most related works analyzed so far make use of two or even three radios for such purposes, as further discussed. In this paper, we detail the Dual-Stack Single-Radio Communication Architecture (DSSRCA), which was first presented in [15]. DSSRCA allows a mobile node (e.g., a UAV) to communicate in a bidirectional manner with a WSN and a Sink node using the same radio. This architecture is composed of a dual stack protocol designed specifically to meet the different network QoS requirements present in UAV-to-WSN and UAV-to-Sink communications, such as best-effort and more reliable communication. DSSRCA suits situations where the mobile node acts as data collector for the WSN. Obtained results confirm the viability of using a single radio transmitter for collecting data from the WSN and flushing such data back to a Sink node, or even for sending telemetry data to a Base Station.