藍(lán)牙特別興趣組最初選擇WiMedia聯(lián)盟的超寬帶技術(shù)作為高速藍(lán)牙的平臺,然而,WiMedia迄今為止尚未獲得所承諾的數(shù)據(jù)吞吐率以及6GHz的工作,從而促使SIG選擇Wi-Fi作為中間過渡解決方案。

在上周由無線電網(wǎng)絡(luò)設(shè)計線出版的一篇文章中,Staccato Communications公司的Roberto Aiello和Siddharth Shetty提出了支持他們的論點的基本原理以及實驗室測量結(jié)果,即如果射頻被用于在藍(lán)牙標(biāo)準(zhǔn)內(nèi)提供更高的數(shù)據(jù)率,它們將與3G蜂窩設(shè)備相互干擾,除非它們在上相距8米以及在上相距16米遠(yuǎn)(見摘錄文章,第20頁；全文見, 文章ID: 206903929)。

作者們的宣稱是根據(jù)他們對g和WiMax之間的干擾進行測試所獲得的測量結(jié)果,這些測量結(jié)果已經(jīng)被收錄在國際電信聯(lián)盟的稱為IMT-2000的3G標(biāo)準(zhǔn)之中。作為比較新的標(biāo)準(zhǔn),WiMax在發(fā)達(dá)市場并未獲得牽引力,但是,作者們主張,在某些應(yīng)用場景中,Wi-Fi也將與其它3G技術(shù)設(shè)備相互干擾。

在無線電設(shè)計社群的一些崗位中,這一關(guān)于存在干擾的告誡引起了工程師的恐慌。在文章發(fā)表之后不久,一位設(shè)計工程師在無線電網(wǎng)絡(luò)設(shè)計線論壇上向測試的方式以及所得到的結(jié)論提出了質(zhì)疑。

例如,那條冗長的帖子暗示,“由Wi-Fi卡所使用的偶極天線不會像帶內(nèi)信號那樣有效地輻射噪聲。Staccato的測試顯示,信號由連接器取出,而不是在天線輻射的后面取出。”

那個帖子還暗示,“斷言干擾導(dǎo)致接收靈敏度下降1-2dB就會造成完全不能接收信號的說法有點杞人憂天。”

幾天以后,Aiello回復(fù)逐條原帖,主張測試流程是正確的,并且它的結(jié)論就是,即使在測試規(guī)劃中實現(xiàn)所建議的改變,干擾問題并不會消失。該論壇的線索是?threadID=1048。

干擾可能會出現(xiàn)的場景高度取決于Wi-Fi射頻的使用情況。

作者們承認(rèn),無線局域網(wǎng)(WLAN)以及IMT-2000 3G設(shè)備在典型情況下不會同時工作。然而,藍(lán)牙和IMT-2000服務(wù)常常將同時工作。那意味著,如果高速藍(lán)牙設(shè)備正在使用交替MAC/PHY (AMP),那么,就有可能進入工作在臨近頻段的IMT-2000的服務(wù)環(huán)境之中。

當(dāng)藍(lán)牙特別興趣組宣布,它打算采用g過渡高速解決方案—當(dāng)6GHz UWB可用時繼續(xù)作為長期解決方案—時,SIG執(zhí)行總監(jiān)Mike Foley表示,g射頻僅僅在需要高速傳輸時才會采用。

翻頁查看英文原文:

WiMedia Alliance member Staccato is claiming that using 20-Mbit/second technology to boost Bluetooth speed will cause interference with nearby WiMax and cellular mobile devices.

The Bluetooth Special Interest Group had originally selected WiMedia's ultrawideband (UWB) technology as the platform for high-speed Bluetooth. But WiMedia's failure thus far to attain promised data throughput rates and 6-GHz operation prompted the SIG to look to Wi-Fi for an interim high-speed solution.

In an article published last week by Wireless Net DesignLine, Roberto Aiello and Siddharth Shetty of Staccato Communications offer both a rationale and laboratory measurements to back up their contention that if 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 at 2.6 GHz and 16 meters apart at 2.3 GHz. (See excerpted article, page 20; find the full article at , article ID: 206903929.)

The authors base their claims on tests measuring the interference between g 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 interference charge has been met with consternation in some quarters of the wireless design community. Shortly after the article was posted, a design engineer posting on a Wireless Net DesignLine 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 in-band signal. The Staccato test shows the signal taken from a connector, not after it is radiated by an antenna."

The post also suggested it is "a bit alarmist to say that interference resulting in more than a 1- to 2-dB 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 invalidated even if the suggested changes in the test plan were implemented. The forum thread is available at ?threadID=1048.

The specific scenario under which interference might occur depends heavily on the utilization of the Wi-Fi radio.

The authors acknowledge that wireless LANs and IMT-2000 3G devices typically don't operate simultaneously. But Bluetooth and IMT-2000 services will often be operating simultaneously. That means that if the high-speed Bluetooth device is using the Alternate MAC/PHY (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 g as an interim high-speed solution-6-GHz UWB continues to be the long-term solution when it becomes available-SIG executive director Mike Foley said the g radio would be utilized only when needed for high-speed transfers.

Jack Shandle (jshandle@) is site editor of Wireless Net DesignLine.