iSCISM: Interference Sensing and Coexistence in the ISM Band

1. Introduction A multitude of commercial devices transmit in the unlicensed 2.4 GHz ISM band, and these devices are likely to interfere with each other. These effects are compounded in highly populated metropolitan areas with large numbers of microwave ovens, Bluetooth devices, cord-less phones, wireless game controllers, and other devices which occupy the ISM band. This contributes to an ever increasing need for effective interference mitigation schemes in Wi-Fi networks. Wideband Interference: Microwave Oven. The most common source of interference in the ISM band is the microwave oven (MWO). Nearly every home, apartment, office, and restaurant in a large metropolitan area contains an MWO, and its operation can severely degrade WiFi transmission. Both residential and commercial MWOs are characterized by a wide-band frequency profile. However, the interference varies in time with a nearly even on-off cycle corresponding to its 60 Hz AC power supply. This corresponds to a period T of approximately 16.7 ms, a key characteristic used in both modeling and identifying MWO signals. Narrowband Interference: Bluetooth. Other than MWOs, most interferers in the ISM band occupy a bandwidth smaller than the approximately 20 MHz WiFi channel. The majority of these devices employ a frequency-hopping spread spectrum (FHSS) method to randomly change between several carrier fre