Hardware Reference
In-Depth Information
ation in public areas such as airports, hotels, rental car pickups, and sporting events.
Bluetooth is also used for a variety of wireless devices on PCs, including printer adapters,
keyboards, mice, headphones, DV camcorders, data projectors, and many others. A list of
Bluetooth products and announcements is available at the official Bluetooth wireless in-
formation website:
www.bluetooth.com
.
Bluetoothdevicesalsousethesame2.4GHzfrequencyrangethatmostWi-Fidevicesuse.
However,inanattempttoavoidinterferencewithWi-Fi,Bluetoothusesasignalingmeth-
odcalled
frequency hopping spread spectrum (FHSS)
,whichswitchestheexactfrequency
used during a Bluetooth session 1,600 times per second over the 79 channels Bluetooth
uses. Unlike Wi-Fi, which is designed to allow a device to be part of a network at all
times, Bluetooth is designed for ad hoc temporary networks (known as
piconets
) in which
two devices connect only long enough to transfer data and then break the connection. The
basic data rate supported by Bluetooth is currently 1Mbps (up from 700Kbps in earlier
versions), but devices that support enhanced data rate (EDR) can reach a transfer rate up
to 2.1Mbps.
The current version of Bluetooth is 4.0, however versions 2.1 and later supports easier
connections between devices such as phones and headsets (a process known as
pairing
),
longer battery life, and improved security compared to older versions. Version 3.0 adds a
high speed mode based on Wi-Fi, while 4.0 adds low energy protocols for devices using
extremely low power consumption.
Interference Issues Between Bluetooth and 802.11b/g/n Wireless
Despite the frequency-hopping nature of Bluetooth, studies have shown that Bluetooth
802.11bg/n devices can interfere with each other, particularly at close range (under 2 meters)
or when users attempt to use both types of wireless networking at the same time (as with a
wireless network connection on a computer also using a Bluetooth wireless keyboard and/or
mouse). Interference reduces throughput and in some circumstances can cause data loss.
Bluetooth version 1.2 adds adaptive frequency hopping to solve interference problems when
devices are more than 1 meter (3.3 feet) away from each other. However, close-range (less
than 1 meter) interference can still take place. IEEE has developed 802.15.2, a specification
for enabling coexistence between 802.11b/g/n and Bluetooth. It can use various time-sharing
or time-division methods to enable coexistence. Bluetooth version 2.1 is designed to minim-
ize interference by using an improved adaptive hopping method, whereas 3.0 and later adds
theabilitytouse802.11radiosforhigh-speedtransfers.CompaniesthatbuildbothBluetooth
and 802.11-family chipsets, such as Atheros and Texas Instruments (TI), have developed
methods for avoiding interference that work especially well when same-vendor products are
teamed together.
