Interconnecting Wireless Sensor and Wireless Mesh Networks: Challenges and Strategies Stefan Bouckaert, Eli De Poorter, Pieter De Mil, Ingrid Moerman, Piet Demeester Ghent University – IBBT – Department of Information Technology (INTEC) – IBCN Gaston Crommenlaan 8/201, B-9050 Gent, Belgium, stefan.bouckaert@intec.ugent.be Abstract— Wireless sensor networks consist of several hun- dredths of simple sensing devices, equipped with a radio. They are typically used for monitoring and automation purposes of large areas. Due to their simplicity, these networks quickly run out of energy, and often have problems regarding scalability and avail- able bandwidth. To solve these issues, current research is mostly limited to the addition of extra sinks to the network, or the use of gateways to request sensor data over the Internet. In this paper, we explore how wireless sensor networks can be combined with wireless mesh networks to obtain a more optimized solution. The mesh network can be used to connect separate sensor networks, to connect sensor nodes with a monitoring platform, or as a scalable backbone for sensor to sensor communication. Additionally, we give an overview of the advantages and disadvantages of existing interconnection techniques between wireless and mesh networks, and propose several new interconnection strategies. Finally, we identify remaining challenges, upon which future research can be based. I. I NTRODUCTION Since wireless network interfaces became cheap and widely available at the beginning of the millennium, there has been an increased research interest in various types of wireless networks and wireless network applications. Within this re- search area, the focus initially was on pure ad hoc net- works, providing solutions at various OSI layers to enable the interconnection of (mobile) wireless nodes without the need for any form of central infrastructure. Because of the wide applicability of wireless networks, several network sub- types emerged that essentially re-use the idea of the self- forming, self-configuring, infrastructureless ad hoc networks, but operate in specific scenarios using specialized types of hardware. Among several sub-types, wireless mesh networks and wireless sensor networks evolved into independent re- search topics. In wireless mesh networks (WMN) [1], the network nodes are considered to be part of the infrastructure and are dedicated to the routing task. The mobility of the mesh nodes is limited or zero, and their processing, memory and bandwidth capacities generally exceed those of traditional ad hoc network nodes. Additionally, the power consumption requirements are often less stringent than those of wireless ad hoc networks. Conversely, wireless sensor networks (WSN) [2] are formed between sensor devices. These devices are characterized by their small size and low cost, but are burdened with relatively low processing and memory capabilities, a limited power supply, and relatively low link bandwidths. While some sensor devices are immobile, other sensor devices are attached to MESH NODE with sensor interface TEMPERATURE SENSOR SELECTOR SWITCH (ACTUATOR) SENSOR NODE Fig. 1. Wireless Sensor Network using a Wireless Mesh Network as a backbone in a home automation scenario. A temperature sensor is directly controlling a HVAC unit, either using path (1) or (2). The same sensor is also used to steer the solar screens, using path (i) or (ii). moving objects and can be highly mobile. Research efforts are mainly located in the field of power efficiency and low-processing routing [3]. Various types of WSNs exist, ranging from simple single hop data collection mechanisms to intelligent multi-hop sensor networks. The latter type of networks allows large scale deployments, and enables the use of advanced mechanisms providing sensor values on demand, or adjusting packet routing according to an application’s need. In the remainder of the paper, the WSN term will refer to intelligent multi-hop sensor networks. In traditional WSNs, sensor data is often collected by a single central device called a sink. This central device is connected to an external management server and/or a database, which authorized users can use to look up the interpreted or raw data. However, by introducing actuator nodes, multi hop WSNs can also exist in isolation from other networks, e.g. a temperature sensor can directly steer a fire alarm, or an actuator node acting as an on/off switch for an HVAC unit. Emerging WSN applications such as Wireless Building Automation [4], Urban Monitoring [5] or Intelligent Trans- portation Systems push the demand for large scale WSNs consisting out of thousands of nodes, dramatically increasing the hop count towards a sink. This issue can be resolved by adding sink nodes to the networks, thereby increasing scalability. By interconnecting the sink nodes, the data is directed towards the management server. Because of its auto- deployment characteristics, a WMN is a convenient way to interconnect the sink nodes. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2009 proceedings. 978-1-4244-4148-8/09/$25.00 ©2009