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Can Bluetooth, Wi-Fi coexist in the future?

Posted: 16 Jul 2002 ?? ?Print Version ?Bookmark and Share

Keywords:bluetooth? wpan? ieee802.11g? wi fi? ofdm?

Many in the industry see Bluetooth and Wi-Fi fighting for the limelight. Some usage models could be viewed as overlapping but Bluetooth (WPAN) is a short-range, cable-replacement technology and Wi-Fi (WLAN) is an extension of a wire LAN, so they are different enough in power consumption, cost, range, usage environment and applications for both to be successful.

Still, there has been some confusion over RF interference between the two, since they both operate in the same 2.4GHz frequency band. And there is even some question about whether the FCC would allow both to operate simultaneously in the same device.

To deal with those perceived barriers, WLAN and WPAN working groups have taken on the task of enabling the two technologies to live together and have built the case for their complementary use. Within the IEEE, the 802.15.2 task group is charged with delivering a "recommended practice" that will describe techniques to allow 802.11b (Wi-Fi) and 802.15.1 (Bluetooth) to coexist. It should be noted that these same techniques should be applicable to the recently approved 802.11g proposal. Within the Bluetooth Special Interest Group, the Coexistence Working Group is quantifying the interaction between Bluetooth and a variety of interference sources and recommending strategies for enhancing its performance.

To date, the techniques evaluated to improve coexistence can be categorized as:

Manual switching

Driver-layer switching

Media access controller (MAC) layer switching

Adaptive frequency hopping

System solution (MAC + physical layer + antenna)

With manual switching, the user must intervene to enable either the Bluetooth or WLAN connection. This can be quickly and simply implemented but does not offer transparent connectivity. In addition, a connection to one type of system must be completely disrupted to connect to the other. Needless to say, it is impossible to operate Bluetooth SCO links while connected to the WLAN using manual switching.

Driver-layer switching is used when Bluetooth and WLAN are in the same platform, though not necessarily sharing common silicon. Here, the driver toggles between the two on a periodic or event-driven basis, suspending operation in the other system by going into a temporary suspend state, called Doze in Wi-Fi and Park, Hold or Sniff in Bluetooth. Since the driver runs under the host OS, it may not have tightly controlled timing, thus, switching between Bluetooth and a WLAN can only be loosely coordinated with data traffic and it would be virtually impossible to coordinate Bluetooth SCO (voice) traffic and WLAN data. Peripherals such as keyboards, joysticks and mice could not use this mode easily because they must be polled. When active, these devices generally are polled at least as fast as the video refresh rate and typically faster.

MAC layer switching takes this concept a step further by switching between Bluetooth and WLAN in the MAC. This MAC--in WLAN specifications--is called the link manager in Bluetooth. Since these functions are typically in the digital baseband circuitry, an integrated solution is implied, at least on the digital side of the chipset. Because many of these functions are in hardware or embedded software, the timing of packet traffic can be controlled more precisely than with driver switching. As a result, MAC layer switching offers better performance than driver-layer switching but still has problems maintaining SCO links during WLAN transfers.

Further study

Adaptive frequency hopping (AFH) is under study by the Bluetooth SIG and IEEE. The best performance-where both systems can operate at full speed in all modes--requires a system approach, combining advanced antenna designs with RF signal processing to excise interfering signals and DSP to boost the signal-to-noise ratio.

While some in the industry believe interference in the 2.4GHz ISM band is a serious problem, it simply represents an opportunity to develop innovative, intelligent, robust wireless systems that deliver data reliably. So Bluetooth and Wi-Fi can operate in close proximity and at full performance.

? Jim Lansford

Business Development Vice President

Mobilian Corp.

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