## 1 Introduction  
Internet of Things (IoT) mainly integrates heterogeneous sensors and actuators for performing tasks in the physical world, using the information obtained from the environment and also considering the specific requirements of applications and services tailored to specific use cases. Various Wireless Sensor Network (WSN) platforms have been proposed to collect sensing information from an observation area and to send to selected network nodes specific actuation commands. The deployment scenarios of WSNs involve the use of a large number of sensors within an observation area to gather a high spatial granularity of measurements that could be then centrally processed and thus provide advanced situation awareness. The high number of sensors also ensures knowledge extraction reliability, even in cases that some sensors are disabled, by using self-healing properties of the WSN communication network. Another important feature that could enhance the capabilities of a WSN is related to the introduction of vehicular sensors (i.e., onboard manned or unmanned vehicles) that could collect measurements on the move, could interact with local clusters of fixed sensors, or could even enable enhanced information collection of specific areas according to triggers and alarms set off by the measurements of the fixed WSN infrastructure. This envisaged heterogeneous WSN involve the combination of heterogeneity in the following features:  
**Sensing Capabilities**: The sensor nodes may be capable of collecting different types of measurements. Examples of measurement/sensing types are the following: temperature, motion, chemicals/gas leaks, video, audio, and energy. **Mobility Capabilities**: Some sensing platforms may be fixed on the ground, whereas some other platforms may be onboard UAVs that will fly over areas of interest to collect data, measurements, and real-time video content. **IoT Access Networks**: The sensor nodes may be communicating with each other with various air interfaces, each having different PHY and MAC protocols that result in different performance metrics such as hop link range, energy efficiency, throughput, etc. The network nodes may be interconnected among each other into different topology formations. They may all connect via a single hop to a central cluster head to form a star-shaped network, or they may establish peer-peer connections among them to formulate appropriate mesh networks that will use multihop paths for the communication of the nodes with a sink or cluster head. Hybrid formations utilizing both star and mesh topology principles may also be considered. Transported Content: The sensing information that will be transported from the end nodes towards the core network and the related processing applications will be of different types. It may involve regular readings (e.g., temperature), event triggers (e.g., motion sensor alerts), and/or streaming content (e.g., audio, video). There may be multiple WSNs operating modes according to the monitored environment conditions and the applications that will be running. For example, a WSN may be operating in a \"regular\" (low power/throughput) mode, obtaining periodic measurements from different sensors scattered over the coverage area. In the case of a specific application requirement or an event trigger, a WSN may reconfigure its operation to \"zoom\"/\"focus\" on a specific location/area and obtain measurements with a higher rate in order to extract more precise knowledge for the observation area. Additionally, another operation mode may be triggered to enable additional sensing functionalities (such as video capturing) that will require a WSN with different topology, higher throughput, and power characteristics. The abovementioned heterogeneous WSN and IoT access network features lead to different performance metric combinations in terms of link throughput, achievable coverage and capacity capabilities, and energy efficiency.