March 2007
doc: IEEE 802.11-07/0468r0
Preferred Channel and DFS
Authors:
Name
Company
Address
Phone
email
Joe Kwak
InterDigital
Bolingbrook, IL
630-739-4159
[email protected]
Jari Jokela
Nokia
Visiokatu 1,
33720 Tampere,
Finland
+358 50 486
0445
[email protected]
Roger Durand
RIM
[email protected]
Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this
document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards
publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in
whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE
standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance
with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for
delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <[email protected]> as early as possible, in written
or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have
questions, contact the IEEE Patent Committee Administrator at <[email protected]>.
Submission
1
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
OUTLINE







Introduction
DFS Regulations
ETSI’s Compliant DFS Specification
Preferred Channel Specification
Comparison of Compliant vs Preferred
Channel specifications wrt regulations
Uniform Spreading requirement details
Conclusions
Submission
2
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Introduction





Use of Preferred Channel for STAs searching for APs for
association saves 80% of battery power.
NOV06 (06/956r2) meeting held straw poll for support of
Preferred Channel with an AP control instead of
distributed control showing 92% support.
JAN06 (07/120r0) meeting presented Preferred Channel
with AP control. Vote to incorporate normative text
showed only 45% support due to concerns about DFS
compliance.
This presentation shows modified Preferred Channel
normative text wording aligned with DFS-compliant
wording from ETSI specification.
This new wording satisfies DFS requirements and
regulations.
Submission
3
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
European DFS Regulations
”Every WAS/RLAN, when operating in the frequency ranges 5 250–5
350 MHz and 5 470–5 725 MHz, shall employ a DFS mechanism with a
Radar Interference Detection function to detect radar signals which have a
level above the interference detection threshold as defined in
Recommendation ITU-R M.1652.
With regard to DFS, a WAS/RLAN device shall operate in either
Master or Slave Mode. WAS/RLAN devices operating in Slave Mode (Slave
Device) can only operate in a network controlled by a WAS/RLAN device
operating in Master Mode (Master Device).
Every Master Device will use the Radar Interference Detection function
in order to check for any co-channel radar signal prior to use a channel but
also during normal operation. In addition to this Radar Interference
Detection function, every Master Device shall also implement a channel
selection mechanism to ensure a near uniform spread of the loading of
available spectrum. The Slave Devices shall not transmit before having
received an appropriate enabling signal from a Master Device. Slave Devices
with a power level of 200 mW e.i.r.p. or above shall have their own Radar
Interference Detection function.”
Verbatim from Decision ECC/DEC/(04)08, 12NOV04, Equiv to FCC ruling.
DFS Regulation
Submission
Uniform Spreading Requlation
4
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
DFS Master Requirements (EN 301 893)





“a) The master device shall use a Radar Interference Detection function in
order to detect radar signals.
b) Before initiating a network on a channel, which has not been identified as
an Available Channel, the master device shall perform a Channel Availability
Check to ensure that there is no radar operating on the channel.
c) During normal operation, the master device shall monitor the Operating
Channel (In-Service Monitoring) to ensure that there is no radar operating
on the channel.
d) If the master device has detected a radar signal during In-Service
Monitoring, the Operating Channel is made unavailable. The master device
shall instruct all its associated slave devices to stop transmitting on this (to
become unavailable) channel.
e) The master device shall not resume any transmissions on this Unavailable
Channel during a period of time after a radar signal was detected. This
period is referred as the Non-Occupancy Period.”
Submission
5
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
DFS Slave Requirements (EN 301 893)



“a) A slave device shall not transmit before receiving an appropriate enabling
signal from a master device.
b) A slave device shall stop all its transmissions whenever instructed by a
master device to which it is associated. The device shall not resume any
transmissions until it has again received an appropriate enabling signal from
a master device.
c) A slave device which is required to perform radar detection (see table
D.3), shall stop its own transmissions if it has detected a radar”
Submission
6
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Uniform Spreading Requirements (EN 301 893)



“Definition: The Uniform Spreading is a mechanism to be
used by the RLAN to provide, on aggregate, a
uniform loading of the spectrum across all devices.
This requires that a RLAN device shall select a channel
out of the list of usable channels so that the probability
of selecting a given channel shall be the same for all
channels.
The probability of selecting each of the usable channels
shall be within 10 % of the theoretical probability. For n
channels, the theoretical probability is 1/n.”
Submission
7
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
ETSI’s Compliant Requirements Summary
1. Master/Slave enabling of transmissions
2. Radar detection for channel availability check
3. Continuous radar detection to monitor
operating channel
4. Uniform Spreading for channel selection
5. Shutdown if radar detected (=channel switch).
Items in RED apply to Preferred Channel, last
requirement already satisfied by TGh Channel
Switch.
Submission
8
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
1. Master/Slave Enabling



Preferred Channel is designed for AP to control
STA transmissions by set/reset of
NetworkAdviceEnabled bit.
No STA shall transmit on Preferred Channel
unless so enabled by AP which sets
NetworkAdviceEnabled bit.
This is eqivalent to ETSI requirement sufficient
for regulatory purposes.
Submission
9
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
2. Radar Detection for Channel Availability
Explicit requirement in new normative text:
“If dot11SpectrumManagementRequired is true, ..the AP
shall periodically monitor the Preferred Channel for
frame transmissions. If no beacons and no network
advice frames are detected on the Preferred Channel,
the AP should perform a channel availability check on
the Preferred Channel to ensure that there is no radar
operating on the channel.”
 “Should” is used because the AP may not have the
resources to detect radar on 2 channels.
 Preferred Channel uses same wording as ETSI.

Submission
10
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
3. Radar Detection for Monitoring Preferred Channel


Explicit requirement in new normative text:
“If an AP has set dot11NetworkAdviceEnabled to true at any STA, the AP shall
ensure that a STA shall use radar interference
detection to monitor the Preferred Channel
for radar per the regulatory requirements.”
Preferred Channel uses same wording as
ETSI.
Submission
11
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
4. Uniform Spreading for channel selection required






Regulation requires “channel selection mechanism to
ensure a near uniform spread.”
In practice this is accomplished simply by randomly
selecting an operating channel.
The Regulation does not specify when the random
channel number is selected or how often the channel is
to be reselected, nor does it address the source of the
required random selection or the restrictions on who
may use the selected channel.
The goal is to provide “near uniform spread”.
Random selection is ETSI’s chosen requirement
mechanism to satisfy the regulation, others exist.
Preferred Channel is randomly selected and satisfies the
spirit and letter of the regulation.
Submission
12
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Uniform Spreading trials with Preferred Channel
All channels randomly selected before use.
Without Preferred Channel
time
1 BSS
chan
With Preferred Channel
1
2
3
4
5
6
7
8
chan
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
chan
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
chan
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
chan
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
chan
1
2
3
4
5
6
7
8
+1 BSS
chan
+1 BSS
chan
+1 BSS
chan
+1 BSS
chan
BSS = 40-70% utilization (typ)
Submission
P.C. = 1- 5% utilization (typ)
13
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Results from Spreading Trials




Use of Preferred Channel produces spectrum spreads no
less uniform (and possibly more uniform) than currently
permitted applications.
Worst case for non-uniform spread occurs with a single
BSS in the regulatory class.
In this case using the Preferred Channel produces a
spread more uniform than conventional operation since
usually occupies two channels instead of one.
All operating channels shall defer and shut down for
radar. The Preferred Channel does this, but further
defers and shuts down for beacons, thus making the
Preferred Channel “available” for all users, according to
the current terms and definitions.
Submission
14
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Conclusions






Preferred Channel is shown to save 75-80% power for
STAs searching for WLAN services (07/0120r0).
New Net Advice transmissions on Preferred Channel
provide a pointer to active BSS channel, and so decrease
the number of scanned channels.
The AP manages all resources for Net Advice
transmissions in a master/slave mode.
The AP acts as enabling master to control channel
transmissions to meet DFS regulations where applicable.
Normative text for Preferred Channel is found in
07/0118r2.
Use of Preferred Channel satisfies all current DFS
regulations.
Submission
15
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
STRAW POLL




Do you support use of Preferred Channel for
Power Saving?
YES
NO
ABSTAIN
Submission
_______
_______
_______
16
Joe Kwak, Jokela, Durand
March 2007
doc: IEEE 802.11-07/0468r0
Motion






Move to include 07/0118r3 into next version of
TGv draft
Moved:_Kwak_____
Second:__________
YES
NO
ABSTAIN
Submission
_______
_______
_______
17
Joe Kwak, Jokela, Durand