Penguin
Note: You are viewing an old revision of this page. View the current version.

Frequency-hopping spread spectrum (FHSS) or direct-sequence spread spectrum (DSSS) technology. FHSS systems are targeted at low-cost low-power low-range low-data-rate applications, and include Bluetooth, HomeRF (SWAP), 2.4GHz DECT (digital European cordless telephone), and FHSS IEEE802.11. The DSSS IEEE802.11b systems are intended for higher-data-rate and higher-range applications, and typically cost more and consume more power. BlueTooth systems are directed at data transfer, such as transferring an e-mail message from a cell phone to a PDA, and support data rates up to 721kbps. HomeRF supports both data and voice transmission, and allows data rates up to 1.6Mbps. Carrying over from its past incarnation at 1.9GHz, 2.4GHz DECT is intended for 2.4GHz cordless phones with a data rate of 552kbps. IEEE802.11 FHSS systems currently support data rates up to 1.6Mbps, but a new 5-MHz channel BandWidth allocation, wideband FH, will allow symbol rates up to 10Mbps. This will let FHSS compete with the current 11Mbps symbol rates supported by DSSS systems.

For FHSS, the 2.40GHz to 2.835GHz ISM band is broken into 75 1MHz channels, with a 2MHz lower guard band and a 3.5MHz upper guard band. All FHSS systems are based on TDMA, with the number of frequency hops per second varying from one standard to another. Bluetooth and DECT utilize Gaussian frequency-shift keying (GFSK) modulation, whereas HomeRF and FHSS 802.11 use 2-level and 4-level frequency-shift keying (FSK).

AddToMe