The IEEE 802.15.4 is one of the low-layer communication standards for personal area networks （PANs） and wireless sensor networks （WSNs）, which may be interfered by other wireless devices in the industrial, scientific and medical （ISM） frequency bands, especially in home environment, such as devices of IEEE 802.1 lb, Bluetooth, cordless telephone, and microwave oven radiation. This article examines the mutual interference effects of 2.4 GHz devices widely deployed at home, via both theoretical analysis and real-life experiment. An analytical model is proposed to estimate the packet error rate （PER） of radio frequency （RF） coexistent networks. The model is verified through a series of experiments. The experimental results also show that Bluetooth has little impact of interference on IEEE 802.15.4 sensor networks, and that the effect of microwave oven radiation on IEEE 802.15.4 sensor devices is tolerable if the device is a few meters away from the oven. Whereas, IEEE 802.1 lb wireless networks can cause problems to IEEE 802.15.4, however the effects can be significantly reduced by a proper channel selection. This article also proposes the interference duration model, which will be helpful in modeling of coexistence simulation. Simulation results show that the stationary scenario obeys the experiments result very well.
Energy efficiency sleep scheduling in wireless sensor networks is one of the most crucial technologies. In this paper, we propose a simple and feasible synchronous node sleeping and waking mechanisms for small scale wireless sensor networks. Sensor nodes are divided into forwarding nodes and listening nodes. Beacon frame containing sleep command from the coordinator can be forwarded to listening nodes via forwarding nodes. All the nodes in the network can enter sleep at about the same time. Through such network synchronization mechanisms, we can realize synchronous sleep and wake of the entire network. Furthermore, a new power control scheme based on routing protocol （PCBRP） in the medium access control （MAC） layer is proposed. It operates with the help of routing protocol and calculates optimal transmission power according to the distance between neighbor nodes. A mapping table including optimal transmission power and node address is established during the route building procedure. The transmission power can be obtained by searching the table with the address of next-hop neighbor in subsequent data transmissions. The proposed mechanisms are implemented in sensor nodes and are evaluated in a test-bed. The analysis and evaluation based on the experimental results confirm that the proposed energy-saving mechanisms are feasible and effective.
