THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
■ BY LOUIS E. FRENZEL W5LEF
WIRELESS TECHNOLOGY OR
JUST TAKEN FOR GRANTED?
New Versions and Applications Keep This
Legendary Technology Alive and Well
You have no doubt heard of Bluetooth — the short-range wireless
technology. It has been around for over a decade now. Yet it seems to be in
the background these days with all the attention focused on the 3G/4G
cellular technologies like Long Term Evolution (LTE) and, of course, the ever
present Wi-Fi. Yet, Bluetooth is alive and well, and continuous progress is
being made in new standards and products. Here is an update on what may
really be the most widely used wireless technique today.
IN CASE YOU FORGOT
62 August 2011
Bluetooth is a short-range radio technology that
operates in the unlicensed 2. 4 GHz industrial-scientific-medical (ISM) band. It has to co-exist with Wi-Fi LANs,
ZigBee networks, cordless phones, and microwave ovens
to mention just a few services that also use this band.
Bluetooth does pretty well with a range up to about 30
feet. The basic output power is 1 m W (0 dBm) but you
can use two other power levels for longer ranges: 2. 5 m W
( 4 dBm) and 100 m W ( 20 dBm). The 4 dBm version is the
most popular, but the higher power version can reach out
to about 100 meters under line-of-sight conditions.
Bluetooth has a raw data rate of 1 Mb/s, but some of
that is overhead that goes to headers and error correction
so the net data rate is 723 kb/s. The modulation is
Gaussian FSK in a frequency hopping spread spectrum
(FHSS) scheme. The carrier hops from one of the 79
channels to another in a random sequence. The hop rate
is 1,600 hops per second for a dwell interval of 625
microseconds. During each hop interval, some data is
transmitted. The FHSS method makes the data very
secure. A more recent upgrade to Bluetooth version 2.1 is
called Enhanced Data Rate (EDR) and uses π/4-DQPSK
modulation that gives a data rate to 2.1 Mb/s. With
8DPSK modulation, the data rate tops out at 3 Mb/s.
Version 3.0 (known as Bluetooth High Speed) uses the
same transmission protocol but employs a Wi-Fi 802.11
radio link to get a data rate up to 24 Mb/s.