Mechanism for Link Quality Measurement May 2007 doc.: IEEE 802.11-07/0691r0 May 2007 Mechanism for Link Quality Measurement Date: 2007-05-04 Authors: 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 stuart@ok-brit.com 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 <patcom@ieee.org>. Michael Souryal, NIST Michael Souryal, NIST

May 2007 doc.: IEEE 802.11-07/0691r0 May 2007 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?”) Michael Souryal, NIST Michael Souryal, NIST

Link Quality Measurement: Uses May 2007 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) Michael Souryal, NIST

Excerpts from IEEE 802.11 TGs Usage Models (11-04/662r16) May 2007 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 Table Usage 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. Michael Souryal, NIST

Link Quality Measurement: Requirements May 2007 Link Quality Measurement: Requirements 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) 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 Michael Souryal, NIST

Possible Mechanisms for Link Measurement May 2007 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 Michael Souryal, NIST

Mechanism Pros Cons Passive Listening Beacons No additional messaging needed Unidirectional measurement 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 Probing 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 Passive Listening Active Probing Unidirectional measurement

Link Measurement Request/Report May 2007 Link Measurement Request/Report based on P802.11k/D7.0 (January 2007) Link Measurement Request Frame Tx Power Max Tx Power MP MP Link Measurement Report Frame TPC Report Element, …, RCPI, RSNI RCPI: Received channel power indicator RSNI: Received signal to noise indicator Michael Souryal, NIST

Sample Data: Bi-directional Filtered SNR Measurements of a Mobile Link May 2007 Sample Data: Bi-directional Filtered SNR Measurements of a Mobile Link 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 Michael Souryal, NIST

May 2007 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 Michael Souryal, NIST

May 2007 Appendix Michael Souryal, NIST

Current Text in P802.11s/D1.03 (April 2007) May 2007 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.” Michael Souryal, NIST

802.11k, “Radio Resource Measurement” May 2007 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 Statisitics Location Configuration Information Neighbor Report Link Measurement Transmit Stream Measurement Michael Souryal, NIST

Raw SNR Measurements of Sample Data May 2007 Raw SNR Measurements of Sample Data Sampling period: 20 ms Michael Souryal, NIST

May 2007 References Michael Souryal, NIST