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IEEE 802.19 TAG, Here is an email
exchange between Bruce Kraemer (802.11 chair) and Mike Foley (Bluetooth SIG
chair) regarding the 40 MHz version of 802.11n, which I thought would be of
interest to the TAG members. Regards, Steve From: ***** IEEE
stds-802-11 List ***** [mailto:STDS-802-11@xxxxxxxx] On Behalf Of Bruce
Kraemer ---
This message came from the IEEE 802.11 Working Group Reflector --- 802.11, Today I received the following letter from Mike Foley, Executive
Director of the Bluetooth SIG. I provided the following response. Mike, Thanks for your note. Our 802.11 TGn task group has been studying
this topic for several years now and I can assure you that it has been a topic
that receives considerable analysis. As I’m sure you are aware many of the
participants in TGn are also participants in the Bluetooth SIG. We are in the
process of evolving our TGn specification with an intent to use the available
2.4 GHz spectrum in a manner that is beneficial to a multitude of parties
including, of course, 802.11 and Bluetooth. The letter you sent was addressed to only Paul and myself. Would
you allow it to be shared with members of 802.11 and in what form, verbal or
written? Regards, Bruce Kraemer Chair WG11 Mike subsequently approved distribution of his letter to the WG. I’m providing this information for discussion on the reflector. We
will also discuss the letter, and perhaps an additional response, during the
March plenary. Regards, Bruce Kraemer Chair WG11 From: Mike Foley
[mailto:mfoley@xxxxxxxxxxxxx] Dear Sirs: The Bluetooth SIG representing over 11,000 member companies
from around the world would like to express our concerns with the introduction
of 40 MHz channels in 2.4 GHz spectrum by the proposed IEEE 802.11n amendment
to IEEE Std 802.11™-2007. The 2.4 GHz spectrum is used by a number of other standards
including IEEE 802.15.1, 802.15.3 and 802.15.4, and has been widely adopted in
the industry (e.g., Bluetooth SIG, Wi-Fi Alliance, and ZigBee Alliance),
utilization of 50% of the available spectrum by a single device significantly
reduces the amount of available spectrum for use by other radio systems sharing
the same spectrum. Some of the radio systems using this spectrum have been
designed in consideration of typical IEEE 802.11 20 MHz channel operation where
channels 1, 6 and 11 are normally used leaving space between those bands for
operation of devices with small channel widths (e.g. IEEE 802.15.4). Other have
been designed using the IEEE Std 802.15.2(tm)-2004 recommended practice that
included Adaptive Frequency Hopping (AFH) allowing coexistence between
frequency hopping devices (e.g., IEEE Std 802.15.1(tm)-2001/5) using 1 MHz
channels and IEEE 802.11 devices using 20 MHz channels. Measurements of the impact of use of 40 MHz channels in the
2.4 GHz spectrum have shown that 66% of the available IEEE 802.15.1 hopping
channels must be removed to prevent interference from a single device using a
40 MHz channel (See 11-08-0992-01-000n-20-40-mhz-11n-interference-on-bluetooth,
11-08-1140-00-000n-11n-40-mhz-and-bt-coexistence-test-results and
11-08-1101-05-000n-Additional-40-MHz-Scanning-Proposal). This is caused by the
channel mask for the proposed 40 MHz signal that is only 28 DB down 40 MHz from
the center frequency. This effectively introduces interference across 75% of
the 2.4 GHz spectrum when the 40 MHz signals are at the top or bottom of the
band. Good detection algorithms built into devices can determine what portions
of the channel to avoid, but the variability of use and compression of the
available number of channels into a small portion of the band reduces noise
immunity and spectrum sharing capabilities below an acceptable level. Over 2.5 Billion Bluetooth wireless devices have been
shipped based on IEEE Std 802.15.1™-2005. Many of these devices implement the
Adaptive Frequency Hopping (AFH) mechanism recommended in IEEE Std
802.15.2™-2003 and subsequently incorporated into IEEE 802.15.1 and all recent
Bluetooth specifications. The Bluetooth SIG has implemented specifications that
coexist well with current IEEE 802.11 based devices and would like to continue
operating in the 2.4 GHz spectrum while coexisting with IEEE 802.11 devices.
Using 40 MHz channels should only be allowed if the 802.11 device ensures that
no other devices are attempting to operating in proximity of those devices so
the 802.11n devices do not severely restrict the operation of the other
devices. Thanks, Mike Foley, Ph.D. Executive Director Bluetooth SIG, Inc. 500 108th Ave NE Suite 250 Bellevue, WA 98004 425-691-3530 _______________________________________________________________________________
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