Dynamic Channel Selection Algorithms for Coexistence of Wireless Sensor Networks and Wireless LANs Mostafa Pakparvar * , Hadi Gharibdoust † , Sofie Pollin † , Lieven Tytgat * * Department of Information Technology, Gent University {FirstName.LastName}@intec.ugent.be † Department of Electrical Engineering - ESAT, KULeuven Hadi.Gharibdoust@student.kuleuven.be Abstract—Due to the advances in wireless technology and spectrum scarcity, unlicensed band heterogeneous networks are growing rapidly. Increasing users of these networks should compete for the shared spectrum. Therefore, interoperability and coexistence of such networks are becoming key issues that require novel media access protocols equipped with dynamic channel selection to avoid harmful interference. In this paper we focus on dynamic channel selection for coexistence of IEEE 802.11 Wireless LAN and IEEE 802.15.4 sensor networks. Dynamic channel selection algorithm can either be implemented on top of an existing wireless sensor network or assisted with an auxiliary spectrum sensing device. In this research couple of dynamic channel selection algorithms have been developed and implemented to evaluate the added value of the auxiliary sensing device. As such, we propose a novel energy-aware metric to detect and quantify the harmfulness of dynamic interference. We also investigated the impact of interference dynamism on algorithms performance and validated the efficiency of the implemented mechanisms by three sets of experiments. Experiments results primarily validate the effi- ciency of both interference mitigation techniques. Besides, these measurements suggest that the auxiliary sensing device is most beneficial for highly complex interference profiles. Index Terms—Wireless sensor networks, ISM band Coexis- tence, Dynamic Spectrum Access, Cognitive Radio, Dynamic Channel Selection I. I NTRODUCTION Advances in wireless technology have paved the way for the emergence of new wireless standards in ISM band where they should compete for the common spectrum. Therefore, interoperability and coexistence are major issues that must be solved for such heterogeneous networks. IEEE 802.11 Wire- less LAN and IEEE 802.15.4 personal area networks (PAN) are examples of ISM band networks with highly dissimilar transmission profiles in terms of coverage, bandwidth, output power, and application requirements. The output power of IEEE 802.15.4 devices is usually lower than 0 dBm [1], while the output power of IEEE 802.11 devices is typically 15 dBm or higher [2]. Spectrum utilization is another dissimilarity where according to the standards, each IEEE 802.11b/g chan- nel occupies at least 4 contiguous IEEE 802.15.4 channels [3]. Application-wise, sensor networks are not demanding in terms of throughput. However, they require high reliability and robustness against attacks or unknown events in case of monitoring applications. In contrast, IEEE 802.11 networks are typically used by a limited number of throughput-intensive applications. Moreover, mobility is one of the most important characteristics of most IEEE 802.11 devices which adds spatial dynamism to the interference profile of the environment. Additionally, new broadband Internet services and appli- cations for advanced WiFi-enabled devices such as smart phones and tablets are attracting more users every day. The high bit rate of novel IEEE 802.11 interfaces and throughput demanding applications all result in burst WiFi traffic which occupies the channel at least an order of magnitude more than a single IEEE 802.15.4 packet. In presence of such WiFi traffic, due to their CSMA/CA mechanism, sensor networks easily enter a blocked state where they are prevented from packet transmission. Consequently, the packet success rate drops drastically as evidenced in our observer reference ex- periment in section IV. This is why the performance of the sensor nodes communication links is compromised when they are present in environments with a broadband WiFi Internet connection. Packet loss is a major issue in wireless sensor networks and directly degrades robustness and energy consumption, two performance metrics of great significance in this context. When a packet is lost in connection-oriented applications, it should be retransmitted to the receiver. Power consumption specifications of CC2420 which is a frequently used IEEE 802.15.4 radio front-end [1], show that a node transmitting or receiving radio packets consumes at least 20 times more power than when it is in low power mode. Thus, high packet error rate (PER) should be avoided on battery constrained wireless sensor nodes. Moreover, in time-sensitive applications such as monitoring and alarm systems, every packet is valuable and it is crucial to preserve data from being lost due to interference. The IEEE 802.15.4 standard proposes channel selection algorithms to be performed by the network coordinator at network initialization; however no specific implementation guideline has been suggested. This mechanism is helpful for static interference profiles, given that the algorithm investi- gates the interference effectively. With the IEEE 802.15.4e standard [3] time slotted channel hopping (TSCH) MAC has been released which facilitates more efficient coexistence and spectrum management. Many algorithms have been developed