Performance analysis of IEEE802.15.4 wireless sensor network to mitigate IEEE802.11 wireless local area network interference

Abstract

Wireless Sensor Networks (WSN) technology is rapidly deployed in applications such as robotic, healthcare, military, environmental monitoring, and other low-power large scale monitoring that requires high data accuracy with possibly minimal latency and data losses. The Quality of Service (QoS) of WSN is often compromised by the interference from other wireless technologies that are high in transmission power and bandwidth such as Wireless Local Area Network (WLAN), Bluetooth, microwave oven, cordless phone and wirelessUSB. The ubiquitous increase in the number of wireless devices leads to the frequency spectrum occupancy issues as various wireless technologies are forced to share the free and unlicensed 2.4GHz frequency band. Compared to other wireless technologies, the interference from the WLAN devices caused a significant packet loss experienced by WSN. This study focuses on investigating the effect of WLAN interference on WSN performance through experimental study. This research provides an empirical study on the effect of WLAN on WSN performance in terms of Energy Detection (ED) and packet loss. A WLAN access point (AP) or router, laptops as end-client and IxChariot software are used to emulate WLAN traffic while Waspmote is used as WSN nodes. Tests had been conducted in two different environments, which is in controlled and uncontrolled environment. Preliminary test found that scan duration need to be set to 3 in order to achieve the best ED value after considering the tradeoff between accuracy and false detection. Result from this study demonstrates that ED is around -84dBm with no packet loss for test conducted without WLAN interferer. Similarly, test conducted with one WLAN interferer (without traffic) shows that there is no packet loss but there is high increase in ED reading that is approximately -44dBm. Besides that, this research found that the density of traffic yield from WLAN network does not significantly affect the ED (around -41dBm) by WSN in comparison to when the WLAN AP is simply turned on without traffic (ED value is around -44dBm). However, the WLAN traffic does affect the WSN packet loss where packet loss increases from 14% to 36% when traffic increased from 10% to 30% in controlled environment. Despite that, further tests revealed that the frequency offset between WLAN and WSN centre frequency did affect the ED by the WSN. The ED value when the frequency offset between WLAN and WSN is less than or equal to 3MHz is approximately -42dBm and the ED value for frequency offset is 8MHz and 13MHz is approximately -54dBm and -68dBm respectively. In addition, this research also studies the performance of WSN for fixed channel allocation. Besides that, this research also proposed a technique to improve WSN performance by performing dynamic channel selection. The technique reduces the WSN packet loss from 7% to approximately 0% packet loss.