I am interested in evaluating interference between cordless phones operating in the 2.4 Ghz band and DSSS WLAN's operating in the same band. If cordless phones use FHSS, do they hop over the entire 83.5 Mhz or over less bandwidth? How does FHSS cordless phones compare to FHSS Bluetooth?
Devices that use frequency hopping spread spectrum (FHSS) work by changing transmission frequencies rapidly to spread data across 83 MHz in the 2.4 GHz ISM band. An FHSS radio transmits on the first frequency of a hop sequence for dwell time, then changes (hops) to the next frequency. The time spent changing from one frequency to another is called hop time. A transmitter and receiver must be synchronized and follow the same hop sequence, dwell time, hop time and carrier width.
Regulatory bodies like the FCC regulate how any kind of FHSS device can use the ISM band by imposing rules like minimum steps per hop sequence and maximum dwell time. Such regulations are aimed at reducing interference between devices using the same modulation technique in the same spectrum.
Organizations like the IEEE and Bluetooth SIG specify physical and link layer standards intended to allow transmitters and receivers produced by different manufacturers to interoperate. For example, the 802.11-1999 standard and the Bluetooth core specification each define different link layer protocol formats and FHSS base hop sequences for use in different countries. Crack open those standards to begin to understand detailed differences between how WLAN and Bluetooth devices hop across the ISM band.
2.4 GHz FHSS cordless phones may comply with FCC rules for devices operating in the ISM band, but you don't buy an FHSS cordless handset from one manufacturer and an FHSS base unit from another. I don't know of a physical/link layer standard that dictates exactly how cordless telephone handsets and base stations communicate with each other, beyond compliance with local regulations regarding use of the 2.4 GHz band.
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