Experimental studies of the ZigBee frequency agility mechanism in home area networks

A normal home environment consists of various wireless technologies, in particular WiFi and ZigBee, which usually operate in the ISM 2.4-GHz band. In addition, some of the home appliances (e.g., a microwave oven) may operate in this crowded ISM band. WiFi-based, ZigBee-based devices and home appliances operating at the same frequency and physical space can cause harmful interference to one another, particularly to ZigBee technology. Therefore, the ZigBee Frequency Agility mechanism is introduced by the ZigBee Alliance to ZigBee networks for resolving such harmful interference. In this paper, we experimentally study the performance of the ZigBee Frequency Agility mechanism using a home area network (HAN) testbed. The measurement results show that this mechanism can effectively overcome interference caused by WiFi-based devices. However, in the extreme case, when all the channels are occupied, the mechanism is not effective as expected. In addition, it is observed that the response time for the ZigBee Frequency Agility mechanism to perform channel switching is depending on packet-error-rate (PER) and send-packet-counter thresholds. Low thresholds can reduce channel-switching time but increases signaling overhead. Thus, in order to obtain optimum performance, self-adaptive PER and send-packet-counter thresholds based on interference level are desired rather than static ones.