Effects, classification and mitigation of external interference in IEEE 802.15.4-based wireless sensor networks at 2.4 GHz

The IEEE Standard 802.15.4 de nes the low power wireless transmission technology behind Wireless Sensor Networks (WSNs) and ZigBee. Since IEEE 802.15.4 is a low power technology, the mitigation of interference is vital to conserve energy and to extend the lifetime of devices. Most of the IEEE 802.15.4 radios operate in the crowded 2.4 GHz frequency band, which is also used by many other technologies. A complete study of the common sources of external interference, namely IEEE 802.11-based Wireless Local Area Networks (WLANs), Bluetooth and microwave ovens, is provided. The effects of these coexisting technologies on IEEE 802.15.4 are investigated and the modeling of the interference is discussed. The possibilities of Energy Detection (ED) (the feature behind Received Signal Strength Indication (RSSI)) and certain Clear Channel Assessments (CCAs) are evaluated. Based on the CCAs, a lightweight interference classi cation algorithm is presented to classify the common external sources of interference in the 2.4 GHz frequency band without demodulation of the inteferers' signals. As the classification algorithm relies on time patterns instead of spectral features, it has no need to change the channel. Thus, it allows the radio both to stay connected to the channel and to receive while the interferer is classified. Furthermore, interference mitigation strategies are reviewed and evaluated with respect to their effectiveness to overcome the three external sources of interference. By combining the interference classification algorithm and the chosen mitigation strategies, Interference-Aware, Self-Adapting (IASA) Medium Access Control (MAC) is developed. This smart interference-mitigating MAC protocol is implemented in ContikiOS and evaluated.