devices are everywhere, and the wireless technologies that make them
possible are fighting for bandwidth to function. The coexistence of
Bluetooth and Wi-Fi in the 2.4-GHz Industrial, Scientific, and Medical
(ISM) band was discussed at the recent Wireless Symposium in San Jose.
Because the simultaneous operation of these two systems can interfere
with one another, the search is on for ways to improve their performance
when they are in close proximity.
As explained by Jim Lansford of Mobilian Corp. (Hillsboro, OR), wireless
personal-area networking (WPAN) and wireless local-area networking (WLAN)
are two technologies headed for significant growth. WPAN applications
primarily include Bluetooth devices such as wireless headsets, wireless
synchronization with PDAs, and other wireless peripherals such as printers.
WLAN applications will likely focus on using Wi-Fi (IEEE 802.11b) for
Internet access, e-mail, and file sharing with speeds of 11 Mb/sec up
to 100 m.
"Coexistence has become a significant topic of analysis and discussion
throughout the industry," says Lansford. "WPAN and WLAN are complementary
rather than competing technologies. With both of them expecting rapid
growth, collocation of Bluetooth and Wi-Fi devices will become increasingly
likely. But, because both technologies occupy the 2.4-GHz frequency
band, there is potential for interference between the them."
Lansford presented techniques for enabling the two technologies to
successfully operate in the same place at the same time. "They create
in-band colored noise for one another. Neither Bluetooth nor Wi-Fi was
designed with specific mechanisms to combat the interference that each
creates for the other. Bluetooth assumes it will hop away from bad channels.
The 802.11b media access layer assumes that if it fails, two Wi-Fi stations
tried to transmit at the same time."
One solution, he says, is to convince FCC to modify its rules such
that Bluetooth could legally hop over a smaller portion of the band.
It is currently required to hop over a minimum of 75 of the 83.5-MHz
available in the 2.4-GHz band. Lansford also presented some practical
solutions, including a ban on 802.11b in environments where Bluetooth
is considered mission critical. General system approaches, as well as
the driver layer, MAC layer, and physical layer were discussed.
"Some in the industry have positioned coexistence in the 2.4-GHz frequency
band as motivation to hasten the migration to 5-GHz WLAN standards such
as 802.11a or HiperLan2," he says. "Coexistence, and ultimately simultaneous
operation between 802.11b and Bluetooth is a highly desirable goal."
Lansford suggests that rather than just focusing on a regulatory solution
or instituting restrictive practices, the indsutry will be best served
through a systems-oriented approach that allows users to take full advantage
of both technologies.