November 2006
doc.: IEEE 802.11-06/1704r0
40 MHz Operation in 2.4 GHz
Date: 2006-11-11
Authors:
Name
Company
Richard van Nee
Airgo Networks
[email protected]
VK Jones
Airgo Networks
[email protected]
Address
Phone email
Srinivas Kandala Airgo Networks
[email protected]
Ali Raissinia
Airgo Networks
[email protected]
Allert van Zelst
Airgo Networks
[email protected]
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Submission
Slide 1
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Abstract
In this presentation, we recap the co-existence issues
regarding 20/40 MHz operation in both the 2.4 Ghz and
5 GHz band.
A proposed set of solutions for 20/40 MHz operation in
the 5 GHz band and 2.4 GHz band are described.
Normative text has been prepared for these solutions
Submission
Slide 2
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
CID’s Addressed
• Subset of CIDs addressed related to 40 MHz operation
in 2.4 GHz band
• 104, 258, 286, 288, 430, 431, 689, 705, 706, 1493, 1560,
1558, 1728, 2848, 3006, 3010, 3471, 3501, 3502, 3602,
4570, 4571, 7010, 7195, 7312, 7313, 7314, 7376, 7871,
7925, 8138, 8282, 8186, 8194
Submission
Slide 3
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Further definition of the
20/40 MHz Issues in Draft 1.0
There are two separate, but related issues:
1.
The current draft does not define normative behavior for
CSMA/CA (i.e. ‘listen before your talk’) for the ‘extension
channel’ in 40 MHz operation
• This issue will lead to interoperability problems with legacy
802.11a/b/g and other .11n equipment
2.
The channel bonded, 2x20 MHz mode as specified leads to a
misaligned use of channels with the majority of the installed base
of legacy .11b/g (which is typically deployed based on a 25 MHz
channel spacing)
• This issue will lead to interoperability problems with legacy
802.11b/g installed base, even if issue #1 is fixed
Submission
Slide 4
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
2.4 GHz Installed base interoperability problematic with
20/40 .11n Operating Modes

Both the Primary and Secondary channel cannot be centered on the widely-used
adjacent 2.4 GHz channels (e.g. channel 1 and 6 or channel 6 and 11)
Extension
40MHz
Channel use
20MHz seperation
Control
Control
Extension
2400
2412
CH1
2417
2422
2427
Widely Deployed
20MHz
Channelization
25MHz seperation
25MHz seperation
2432
2437
2442
2447
CH6
2452
2457
2462
2467
2472
2483.5
CH11

The Primary and Secondary channels would be 1 and 5, or 6 and 2 for example;
i.e. misaligned by 5 MHz

In the misaligned channel, there will be no proper defer behavior leading to a high
collision rate
Submission
Slide 5
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Requirements for a Proposed Solution
• CCA sensing on both Primary and Secondary Channel
• Address the 5 MHz offset issue, to ensure ‘good
neighbor’ behavior with the fast majority of the legacy
installed base of .11b/g devices
Litmus test for Proposed Solutions:
“Will the solution protect a single .11g VOIP call in an
OBSS that overlaps in the Secondary channel?”
Submission
Slide 6
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Overview of the Proposed Solution for 5 GHz band (1/2)*
• Before commencing any 40MHz transmission, a STA shall
sense CCA on both Primary channel and Secondary
channel
– Secondary Channel CCA shall be deemed busy during Tx or Rx of a
20 MHz frame in Primary Channel
– TX of 40 MHz frame only if Secondary channel has been idle for at
least a DIFS
– When TXOP obtained for a 20 MHz transmission, STA shall not
transmit 40 MHz frames during this TXOP
* A key strawpoll in Melbourne showed strong support for this proposed solution
Submission
Slide 7
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Overview of the Proposed Solution for 5 GHz Band (2/2)*
• CCA sensitivity
– Receiver of a 20/40 MHz STA shall provide CCA on both the primary
and secondary channels
– CCA busy for:
• Start of a valid 20 MHz transmission** in the Primary channel at Rx level
> -80dBm; primary CCA busy
• Start of a valid 40 MHz transmission in the Primary and Secondary
channel at Rx level > -77 dBm; both primary and secondary CCA busy
• 20 MHz primary CCA for any signal > -60 dBm (ED)
• When primary CCA Idle, Secondary Channel CCA for any signal >
-60 dBm (ED)
• For a 40 MHz transmission, both primary and secondary channel CCA for
any signal level > -57 dBm (ED)
* A key strawpoll in Melbourne showed strong support for this proposed solution
** Valid transmission = A transmission that is detected as a .11 waveform, and for which a preamble has been decoded
Submission
Slide 8
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
The Proposed Solution for 2.4 GHz Includes an
Optional Legacy Duplicate DSSS Mode
•
Can be used to transmit a CTS-to-self or RTS-CTS that
can be received by legacy 11g devices, even with a
carrier offset of 5 or 10 MHz
•
This will ensure proper defer behavior in the 2.4 GHz
band regardless what channels are used
•
Duplicate DSSS signal uses a 20 MHz spacing just like
the existing duplicate non-HT OFDM rates.
Submission
Slide 9
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Example Transmitter For Duplicate DSSS
j
Generate
baseband
legacy DSSS
signal
Shift by
+10 MHz
DAC
To RF
Shift by
-10 MHz
• This is exactly the same structure that can be used for the
existing duplicate non-HT OFDM rates
Submission
Slide 10
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Duplicate DSSS Spectrum
10,
Power Spectral Density [dB]
0,
-10,
-20,
-30,
-40,
-50,
-60,
-70,
-80,
-40,
-30,
-20,
-10,
0,
10,
Frequency [MHz]
20,
30,
40,
• Spectrum falls well within 11n 40 MHz mask
• No changes required in filtering
Submission
Slide 11
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Proposed Additions* for 2.4 GHz operation (1/2)
For 20/40 MHz operation:
• Mandatory sensing of transmissions in the Secondary channel
that are not part of a 40 MHz operation in the same BSS
–
•
Per CCA sensitivity levels as described in the slide summarizing the
consensus solution for the 5 GHz band
If secondary channel is not idle, STA shall immediately do one of
the following:
–
For Non-AP STAs, either:
1. Switch to 20 MHz only mode
Or:
2. Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHz-duplicateDSSS rate prior to any 40 MHz transmission (to set NAV of devices operating
in Secondary channel)
• When secondary “channel busyness” persisted for a configured
percentage value (e.g. 10, 20, 40%) over a configured time then non-AP
STA SHOULD switch to 20 MHz only mode
* In addition to the solution as described in the slide summarizing the consensus solution for the 5 GHz band
(i.e., a device operating in 2.4 GHz band should behave according to elements described for 5 GHz band + contents of this slide).
Submission
Slide 12
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Proposed Additions* for 2.4 GHz operation (2/2)
–
For AP STAs, either:
1. Switch the BSS:
• Switch BSS to 20MHz only mode
• Remain in 20/40 mode but switch BSS to different 40 MHz channel set
Or:
2. Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHz-duplicateDSSS rate prior to any 40 MHz transmission
• When secondary “channel busyness” persisted for a configured
percentage value (e.g. 10, 20, 40%) over a configured time then AP STA
SHOULD switch to 20 MHz only mode
–
STA may switch back from 20 MHz only mode to full 20/40 MHz
mode after the duration of ‘dot 11SecondaryOBSSSwitchTime’
(configurable parameter)
* In addition to the solution as described in the slide summarizing the consensus solution for the 5 GHz band
(i.e., a device operating in 2.4 GHz band should behave according to elements described for 5 GHz band + contents of this slide).
Submission
Slide 13
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
“Will the solution protect a single .11g VoIP call
in an OBSS that overlaps in the Secondary
channel?”
• Proposed solutions:
– Immediately switch back to 20 MHz only or switch BSS to another
40 MHz channel:
• Yes it will protect VoIP call, but may not always be the most efficient
solution
– Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHzduplicate-DSSS rate prior to 40 MHz transmissions:
• Yes, it will protect VoIP call in secondary channel (even at an offset of
5 or 10 MHz), and benefits of using 40 MHz modes in the 2.4 GHz
channel can be achieved.
An alternative solution may be to exclude the use of 40 MHz modes in
the 2.4 GHz band in the standard altogether. However, it appears
unrealistic to assume that this will prevent the marketplace
proliferation of products which operate in 40 MHz modes in the 2.4
GHz band.
Submission
Slide 14
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
BACKUP SLIDES
Submission
Slide 15
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
11b rates With Channel Offset
Two 1 Mbps networks
on Channel 1, second
network turned on after
20 seconds
Two 1 Mbps networks
on Channels 1 and 2,
second network turned
on after 20 seconds
Networks properly defer in the presence of a channel offset
when using 11b Barker rates – they share fairly
Submission
Slide 16
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Channel Utilization USA
Percentage of AP's using a given channel in the
2.4GHz band in the US
70%
64%
60%
50%
40%
30%
20%
16%
12%
10%
1%
1%
1%
0%
2
3
4
5
1%
2%
1%
2%
7
8
9
10
0%
0%
0%
12
13
14
0%
1
6
11
Channel
Submission
•
Total of 1088 Access Points
•
Measurements taken in San Francisco and Silicon Valley
using the Netstumbler tool
Slide 17
Richard van Nee, Airgo Networks
November 2006
doc.: IEEE 802.11-06/1704r0
Channel Utilization Europe
Percentage of AP's in a given channel in the 2.4GHz
band in sample European Countries
35%
32%
30%
25%
21%
20%
17%
15%
10%
8%
7%
4%
5%
3%
2%
3%
1%
1%
4
5
1%
1%
0%
0%
1
2
3
6
7
8
9
10
11
12
13
14
Channel
•
Total of 1722 Access Points
•
Measurements taken in Netherlands, Belgium and Italy
Submission
Slide 18
Richard van Nee, Airgo Networks