IEEE 802.15.4 Wireless Sensor Networks (WSNs) share the 2.4 GHz Industrial, Scientific, and Medical (ISM) license-free band with many other wireless technologies such as IEEE 802.11b/g Wireless Local Area Networks (WLANs). Because of the low-power, however, IEEE 802.15.4 WSNs are potentially vulnerable to the interference introduced by the other wireless technologies such as IEEE 802.11b/g WLANs, which have much higher power. Particularly, in the presence of heavy interference, IEEE 802.15.4 nodes can hardly get a chance to access the channel, which could result in discarding a large amount of packets. In this paper, we propose a decentralized approach to help IEEE 802.15.4 nodes mitigate interference. By adaptively and distributively adjusting Clear Channel Assessment (CCA) thresholds of IEEE 802.15.4 nodes in the presence of heavy interference, the approach can substantially reduce the amount of discarded packets due to channel access failures, and therefore significantly enhance the performance of IEEE 802.15.4 WSNs. The approach is robust, responsive and easy to be implemented at a low cost. The effectiveness of the approach is validated by OPNET simulation.@en

As ZigBee networks operate on the license-free 2.4 GHz Industrial, Scientific, and Medical (ISM) frequency band, coexistence issues arise because many other wireless technologies such as IEEE 802.11b/g Wireless Local Area Networks (WLANs), Bluetooth, cordless telephones, etc., also use the same frequency band. To mitigate interference, ZigBee specification proposes a feature called frequency agility, which refers to the ability of ZigBee networks to change the operational channel in the presence of interference. However, for a large-scale ZigBee network, changing the whole network operational channel to an idle one, may be neither appropriate if there is only local interference nor possible if there is no any single idle channel available globally. In this paper, we propose a distributed adaptive multi-channel MAC interference-avoidance protocol, which enables a conventional large-scale single-channel ZigBee network to distributedly, adaptively and partially change the operational channel in order to avoid local interference. OPNET simulation results show that the protocol can efficiently and effectively improve the ZigBee network robustness and therefore the coexistence performance.@en