ABSTRACT
Wireless sensor network (WSN) consists of a large number of sensor nodes
distributed in the monitoring area, and the nodes form a self-organizing multi-hop
network via short-range wireless communication. With different types of sensors, WSN
can monitor the surrounding environment, including temperature, humidity, light
intensity, pressure, sound, and many other physical phenomena interested to human
beings.
As more and more wireless devices work in the 2.4GHz ISM band, the problem of
interference has aroused worldwide attention. The interference on WSN is mainly from
three aspects: first, intra-network interference; second, external interference from the
other wireless devices; third, interference from geographically overlapping WSN
networks. Because MAC protocol will directly affect the network's overall performance,
compared with the single-channel MAC protocol, multi-channel MAC protocol can
dynamically distribute channel according to the link quality, which has a strong
anti-interference ability.
This paper studies the existing multi-channel protocol, and analyses their principles
and the distinction between each other. To mitigate the effect of WLAN interference on
WSN, this paper combines CTP with anti-interference strategy and proposes a
multi-channel protocol based on TinyOS, including channel distribution, the handshake
mechanism, anti-interference strategy and the related components definition. We
experimentally investigate the effects of WLAN interference on packet delivery
performance in WSN. Preliminary experimental study verifies the CTP protocol
adaptive mechanism, but also shows the impact of WLAN on WSN. When RF output
power is less than -10dBm, a wireless sensor network cannot construct successfully;
when the center frequency of a WSN overlap that of a WLAN, the ratio of beacons to
total traffic in the WSN and the average hops increase significantly. We also test the
multi-channel protocol; the result shows that RSSI will drop because of WLAN
interference, but after channel diversity the RSSI will gradually distribute between
-45dBm and -60dBm again, which can show that the multi-channel protocol plays a role
in the resistance of WLAN interference.
Key word: Wireless sensor network, Multi-channel, Interference,
CTP , MAC protocol