Differences between version 5 and predecessor to the previous major change of FHSS.
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| Newer page: | version 5 | Last edited on Saturday, July 23, 2005 12:19:03 pm | by CraigBox | Revert |
| Older page: | version 4 | Last edited on Wednesday, October 22, 2003 10:10:49 am | by StuartYeates | Revert |
@@ -1,5 +1,12 @@
-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
.
+[
FHSS] is
an [Acronym
] for ''Frequency
-Hopping Spread Spectrum''
.
-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).
+FHSS is a spread-spectrum method of transmitting signals
, by rapidly switching a carrier among many frequency
channels, using
a pseudorandom sequence known
to both transmitter
and receiver
. A spread
-spectrum transmission offers three main advantages over a fixed
-frequency transmission:
-AddToMe
+# Spread-spectrum signals are highly resistant to noise and interference. The process of re-collecting a spread signal spreads out noise and interference, causing them to recede into the background.
+# Spread-spectrum signals are difficult to intercept. A Frequency-Hop spread-spectrum signal sounds like a momentary noise burst or simply an increase in the background noise for short Frequency-Hop codes on any narrowband receiver except a Frequency-Hop spread-spectrum receiver using the exact same channel sequence as was used by the transmitter.
+# Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.
+
+FHSS was used in the original [802.11] standard, but was replaced with [DSSS].
+
+* [FHSS at Wikipedia|http://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum]
+* [FHSS at wireless-nets.org |http://www.wireless-nets.com/articles/whitepaper_spread.htm ]
