Study on Distance of Interference Sources on Wireless Sensor Network

In this paper interference of WiFi on wireless sensor networks (WSN) is studied. Indeed, these networks share the 2.4 GHz industrial, scientific and medical (ISM) band with Bluetooth, WiFi, wireless USB, cordless phone and microwave ovens. How large is the interference between these devices? In all these standards different modulation techniques like frequency hopping, direct-sequence spread spectrum (DSSS) and orthogonal frequency-division multiplexing (OFDM) are involved. The frequency spectrum of a WiFi interferer is measured. We will show that the frequency overlap of 802.11g on WSN is greater than that of a 802.11b channel. Next the effect of a WiFi interferer on a WSN will be studied. We will present experimental graphs for minimal separation of a 802.11b/g interferer and a ZigBee receiver. For the same packet error rate some transmitters need to be further away from ZigBee receiver than others. In this paper it is shown with measurements that lowering the throughput of 802.11g (OFDM) to span a longer distance will have a negative effect on the quality of the ZigBee link. Based on these interference results it is possible to develop a method for co-operative and/or non co-operative interference suppression.