Sparks fly over Wi-Fi/Bluetooth combo
A WiMedia Alliance company claims that using 802.11 20-Mbits/s technology to give Bluetooth a big speed boost will cause interference with nearby WiMAX and cellular mobile devices.
WiMedia’s UWB technology had originally been selected by the Bluetooth SIG as the technology platform for high-speed Bluetooth. But WiMedia’s failure to attain promised data throughputs and 6 GHz operation prompted the SIG to look to Wi-Fi for an interim high-speed solution.
In an article published by WirelessNetDesignline earlier this week, Roberto Aiello and Siddharth Shetty of Staccato Communications offered both a rationale and laboratory measurements to back up their contention.
According to Aiello and Shetty, if 802.11 radios are used to provide higher data rates within the Bluetooth standard, they will interfere with 3G cellular devices unless they are located approximately 8 meters apart for 2.6 GHz and 16m apart at 2.3GHz.
The authors based their claims on tests measuring the interference between 802.11g and WiMAX, which has been included in the International Telecommunication Union’s 3G designation codified as IMT-2000. A relatively new standard, WiMAX has not gained traction in developed markets but the authors contend that in certain usage scenarios Wi-Fi would interfere with other 3G technologies as well.
The article is available at Testing raises concerns over 802.11-based high-speed Bluetooth.
The interference charge has been met with consternation inside parts of the wireless design community. Shortly after the article was posted, a design engineer posting on a WirelessNetDesignline forum took issue with the way the test was conducted and its conclusions.
The lengthy post suggested, for example, that “The dipole antenna used by the Wi-Fi card would not radiate the out of band noise as efficiently as the inband signal. The Staccato test shows the signal taken from a connector not after it is radiated by an antenna.”
Among other comments, the post also suggested that “It seems a bit alarmist to say that interference resulting in more than a 1-2db receive desensitization will result in a complete inability to receive a signal.”
A few days later, Aiello answered the original post point by point, contending that the test procedure was proper and that his conclusion that interference will be a problem would not be invalided even if the suggested changes in the test plan were implemented.
The forum thread is available at www.techonline.com/tigforums/thread.jspa?threadID=1048 .
The specific scenario under which interference might occur depends heavily on the utilization of the Wi-Fi radio.
The authors acknowledge that WLANs and IMT-2000 devices typically don’t operate simultaneously. But Bluetooth and IMT-2000 services will often be operating simultaneously. This means that if the high-speed Bluetooth device is using the 802.11 AMP, it is likely to be running in an environment with IMT-2000 services operating in nearby frequency bands.
When the Bluetooth SIG announced its intention to use 802.11g as an interim high-speed solution—6GHz UWB continues to be the long term solution when it becomes available—SIG Executive Director Mike Foley said the 802.11g radio would be utilized only when needed for high-speed transfers.
Jack Shandle