doc.: ieee 802.11-07/0650r0 submission may 2007 michael souryal, nistslide 1 mechanism for link...
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May 2007
Michael Souryal, NIST
Slide 1
doc.: IEEE 802.11-07/0650r0
Submission
Mechanism for Link Quality Measurement
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Date: 2007-05-11
Name Company Address Phone email Michael Souryal NIST 100 Bureau Dr.,
Stop 8920 Gaithersburg, MD 20899-8920
+1 301 975 4342
Nader Moayeri NIST 100 Bureau Dr., Stop 8920 Gaithersburg, MD 20899-8920
+1 301 975 3767
Authors:
May 2007
Michael Souryal, NIST
Slide 2
doc.: IEEE 802.11-07/0650r0
Submission
Abstract
This presentation discusses the need for a standard mechanism to obtain link quality measurements, in particular to obtain timely bi-directional link measurements in mobile mesh networks. It compares alternative mechanisms for link quality measurement and recommends adoption of the Link Measurement Request/Report capability specified by TGk.
(This presentation is in response to the strawpoll taken at the March 2007 meeting in Orlando: “Should IEEE 802.11s TG consider reviewing specifications about certain aspects of a multi-hop breadcrumb communication system, such as a real-time channel assessment and breadcrumb deployment strategy, based on IEEE 802 PHY/MAC protocols?”)
May 2007
Michael Souryal, NIST
Slide 3
doc.: IEEE 802.11-07/0650r0
Submission
Link Quality Measurement: Uses
• Computation of link metric, and ultimately path metric, for path selection– Link state defined by two parameters
r : current bit rate in use
ef : frame error rate at bit rate r
– Airtime cost metric
where Oca, Op, and Bt are constants defined in clause 11A.5
• Maintaining connectivity during mesh network deployment (e.g., Public Safety and Military usage models)
f
tpcaa er
BOOc
1
1
May 2007
Michael Souryal, NIST
Slide 4
doc.: IEEE 802.11-07/0650r0
Submission
Excerpts from IEEE 802.11 TGs Usage Models (11-04/662r16)
• From Description of Public Safety Usage Model“Communications for public safety networks are mostly outdoors, but may include communicating with first responders inside buildings (potentially deep inside with contact only by multi-hop relaying).... Node mobility, dynamic variations in radio propagation, equipment/power failures, etc. make network self-configuration and self-management essential in these scenarios.”
• From Usage Model Characteristics TableUsage Model Category Mesh AP/ Point Mobility
Public Safety Mix of fixed radios (e.g. on poll tops) and mobile nodes deployed in emergency vehicles and carried by emergency workers.
Military May have a few stationary radios … and mobile nodes deployed in combat vehicles, ships or carried by dismounted troops.
May 2007
Michael Souryal, NIST
Slide 5
doc.: IEEE 802.11-07/0650r0
Submission
Link Quality Measurement: Requirements
• Measurement procedure that works across vendors– Measurement mechanism not specified in P802.11s/D1.03 (April
2007)
– In particular, no mechanism is defined for bi-directional link quality measurement Important for detecting asymmetric links
• Timely measurements for mobile mesh links– Channel coherence time: rough measure of time duration over
which channel impulse response is invariant
– Example: 2.4 GHz, 1.2 m/s (pedestrian speed)
ms 104m/s 2.1
m 125.0
vTc
May 2007
Michael Souryal, NIST
Slide 6
doc.: IEEE 802.11-07/0650r0
Submission
Possible Mechanisms for Link Measurement
Need to receive a frame in order to make a measurement.
Possible means for obtaining link measurements include:
• Passive listening to– Beacons
– RA-OLSR HELLO messages
– Other traffic (e.g., data transmissions)
– 802.11k Measurement Pilot frames
• Active probing with– Probe Request/Response
– 802.11k Link Measurement Request/Report
Mechanism Pros Cons
Pa
ssive L
isten
ing
Beacons
No additional messaging needed
Un
idirection
al m
easure
me
nt
Not all MPs continuously beacon
RA-OLSR HELLO messages
RA-OLSR is optional
Other traffic (e.g., data messages)
Measurement availability not guaranteed
802.11k Measurement Pilot frames
More efficient and frequent than beacons
Overhead for entire network
Active
Pro
bing
Probe Request/ Response
Application can control measure-ment interval
On-demand measurement, only when and where needed
Not all MPs respond to Probe Requests
802.11k Link Measurement Request/Report
Bi-directional measure-ment
Additional message overhead
Pa
ssiv
e L
iste
nin
gA
cti
ve P
rob
ing
Un
idir
ect
ion
al
me
asu
rem
en
t
May 2007
Michael Souryal, NIST
Slide 8
doc.: IEEE 802.11-07/0650r0
Submission
Link Measurement Request/Report
based on P802.11k/D7.0 (January 2007)
MP MP
Link Measurement Request Frame
Tx PowerMax Tx Power
Link Measurement Report Frame
TPC Report Element,…, RCPI, RSNI
RCPI: Received channel power indicatorRSNI: Received signal to noise indicator
May 2007
Michael Souryal, NIST
Slide 9
doc.: IEEE 802.11-07/0650r0
Submission
0 20 40 60 80 100 120 140 160 18010
20
30
40
50
60
70
80
Time (s)
Filt
ere
d S
NR
(d
B)
Link A->B
Link B->A
• Fixed STA “A”, mobile STA “B”• “B” carried down 110 m corridor and
back at ~ 1.2 m/s• Sampling period: 100 ms• Filter: Uniform moving average of
last 20 samples (2 s filter)• Data rate: 2 Mbps
Sample Data: Bi-directional Filtered SNR Measurements of a Symmetric Mobile Link
May 2007
Michael Souryal, NIST
Slide 10
doc.: IEEE 802.11-07/0650r0
Submission
Sample Data: Bi-directional Filtered SNR Measurements of an Asymmetric Mobile Link
0 20 40 60 80 100 120 140 160 18010
20
30
40
50
60
70
80
Time (s)
Filt
ered
SN
R (
dB)
Link A->B
Link B->A
• Fixed STA “A”, mobile STA “B”• “B” carried down 110 m corridor and
back at ~ 1.2 m/s• Sampling period: 100 ms• Filter: Uniform moving average of
last 20 samples (2 s filter)• Data rate: 2 Mbps
May 2007
Michael Souryal, NIST
Slide 11
doc.: IEEE 802.11-07/0650r0
Submission
Summary
• Mobile mesh networks (e.g., public safety and military usage models) require the ability to measure link quality on-demand– For up-to-date link metric evaluation in time-varying channels
– To facilitate maintaining connectivity during rapid deployment of MPs
• Standard mechanism for link quality measurement ensures operation across vendors
• Link Measurement Request/Report capability specified by TGk satisfies these requirements– Permits on-demand, bi-directional link measurement
May 2007
Michael Souryal, NIST
Slide 12
doc.: IEEE 802.11-07/0650r0
Submission
Appendix
May 2007
Michael Souryal, NIST
Slide 13
doc.: IEEE 802.11-07/0650r0
Submission
Current Text in P802.11s/D1.03 (April 2007)
• In 11A.5.2, “Local link state maintenance procedures”:
“The peer MP with the larger MAC address determines the link quality.”
“An MP shall update the values in its neighbor MP table whenever a local link state announcement message is received.”
May 2007
Michael Souryal, NIST
Slide 14
doc.: IEEE 802.11-07/0650r0
Submission
802.11k, “Radio Resource Measurement”• Provides standard measurements across vendors of radio link
performance and the radio environment• Addresses mobility requirements by speeding up handoffs through
collection of pre-handoff information• Request/response measurements:
– Beacon– Measurement Pilot– Frame– Channel Load– Noise Histogram– STA Statistics– Location Configuration Information– Neighbor Report– Link Measurement– Transmit Stream Measurement
May 2007
Michael Souryal, NIST
Slide 15
doc.: IEEE 802.11-07/0650r0
Submission
50 50.5 51 51.5 5218
20
22
24
26
28
30
32
34
36
Time (s)
SN
R (
dB
)
Link B->A
Link A->BSampling period: 20 ms
Raw SNR Measurements of Sample Data (Symm. Link)
May 2007
Michael Souryal, NIST
Slide 16
doc.: IEEE 802.11-07/0650r0
Submission
References
• IEEE P802.11s/D1.03, “ESS Mesh Networking,” April 2007.
• IEEE P802.11-04/662r16, “IEEE 802.11 TGs Usage Models,” W. Steven Conner, January 18, 2005.
• T. S. Rappaport, Wireless Communications: Principles & Practice. Upper Saddle River, NJ: Prentice Hall PTR, 1996.
• IEEE P802.11k/D7.0, “Radio Resource Measurement,” January 2007.