Application Notes

Monitoring Interference app note

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Application Note Monitoring Interference in the 2.4 GHz ISM Band with a Real-Time Spectrum Analyzer A Brief History of the 2.4 GHz ISM Band Since the 1940s, the International Telecommunication Union (ITU) has been in charge of allocating unlicensed spectrum for use by applications including communications, heating, and research. Regional regulators, such as the FCC in North America and ETSI in Europe, are responsible for spectrum management and licensing with their territories. While these regional regulators may place local restrictions on the power density of devices in these bands to facilitate spectrum reuse and high user density, typically devices developed for use in specific bands (e.g., 2.4 GHz ISM band) can be legally operated globally. In the late 1990s, two emerging technologies adopted the 2.4 GHz ISM band for low power consumer connectivity – IEEE 802.11 (Wi-Fi) and Bluetooth®. These technologies rapidly achieved massive consumer acceptance as they became the standard technologies adopted by manufacturers of cell phones, headsets, PCs, point-of-payment credit card readers, and children's toys. More recently, other markets have also adopted the 2.4 GHz ISM band for use by Wi-Fi and Bluetooth enabled smart meter reading and drone controllers. Market analysists estimate that there are over 10 billion Bluetooth and Wi-Fi devices active in the world today, and that adoption rates continue to grow as new applications are established 1 . Montioring for Interference at 2.4 GHz With so many active devices in circulation, it is important to be able to monitor the spectrum in any given location to understand what user experience can be expected. A typical public space, such as a transport hub, conference center, or shopping mall, may have thousands of active users of the 2.4 GHz spectrum at any given time. Even domestic homes may see Wi-Fi access points from a number of neighboring properties. In domestic situations there is the additional possibility that a microwave oven may be in use, which often leak significant power across the 2.4 GHz band. In these situations, user density can restrict throughput and ultimately user experience. 802.11 Wi-Fi Radio Behavior in the 2.4 GHz ISM Band The IEEE introduced the first 802.11 standard in 1997, and was quickly followed up with 802.11b (2.4 GHz) and 802.11a (5 GHz) in 1999. 802.11b supported up to 11 Mbps maximum transmission speed using direct-sequence spread spectrum (DSSS) modulation. In 2003, the introduction of 802.11g boosted these data rates to 54 Gbps using orthogonal frequency-division multiplexing (OFDM) modulations. 1 "Wi-Fi Alliance® publishes 2018 Wi-Fi® predictions", Wi-Fi Alliance, https://www.wi-fi.org/news-events/newsroom/wi-fi-alliance-publishes-2018-wi-fi-predic- tions. Bluetooth Market Update, Bluetooth SIG, https://www.bluetooth.com/blog/the-state-of-bluetooth-in-2018-and-beyond/

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