1. Interference Diagnostics
March 2007
IEEE /0xxxr0
Interference Diagnostics
Authors:
Name
Company
Address
Phone
Joe Kwak
InterDigital
Bolingbrook, IL
Jari Jokela
Nokia
Visiokatu 1, Tampere, Finland  
Roger Durand
RIM
Notice: This document has been prepared to assist IEEE 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
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures < 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 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at
Joe Kwak( InterDigital), Jokela, Durand
Submission

2. Joe Kwak( InterDigital), Jokela, Durand
OUTLINE
Introduction
Interference definitions
New Interference Measurands
Measurement details
Normative text framework
Usefulness of Diagnostic Alert
Conclusions
Joe Kwak( InterDigital), Jokela, Durand
Submission

3. Joe Kwak( InterDigital), Jokela, Durand
March 2007
IEEE /0xxxr0
Introduction
The detection and measurement of RF Interference (RFI) is important for managing radio and network resources.
Hi RFI levels degrade link performance, causing errors and retransmissions, reduced data rates and decreased radio range.
TGv has incorporated features to detect and report on internal interference: Co-located Interference Request/Report.
This proposal considers a new Management Diagnostic for external interference reporting.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak( InterDigital), Jokela, Durand
Submission

4. What is RF Interference
Not thermal noise
Not the intended receive signal
But everything else: Local RFI from nearby electronics (electric motors, microwaves), remote in-band users of other technologies (bluetooth, radars) , remote in-band users of in nearby BSSs, space radiation, etc.
Characterized as:
Transient or steady state (SS)
Wide area (affecting all STAs iin BSS)
Local (affecting some STAs in BSS)
Joe Kwak( InterDigital), Jokela, Durand
Submission

5. Interference Measurement
No easy direct measurement for RFI
Lab/field installation measurements usually conducted by “controlling” RFI sources and measuring received power with/without interference. Not practical for operating networks.
RFI presence may be indirectly inferred from other directly measurable parameters: ANPI, ChannelLoad, FER
RFl is summed with noise in ANPI (only when RFI < EDT).
RFI may limit channel access (RFI >EDT) and increase ChannelLoad.
RFI decreases RSNI and may increase frame errors and retransmissions.
This proposal uses existing measurements to detect RFI.
Joe Kwak( InterDigital), Jokela, Durand
Submission

6. Joe Kwak( InterDigital), Jokela, Durand
March 2007
IEEE /0xxxr0
New RFI Measurands ID
Measurand
Use
Description
Pros/Cons 1
Quiet_ANPI Null_Ant_ANPI
AP & STA
Quiet_ANPI= No activity ANPI (3AM?)
Null_Ant_ANPI= Dummy load or config
Detects SS RFI as background level.
Some STAs can’t switch to null ant. Disruptive to quiet all BSSs for measurement. 2
ANPI Quiet_ANPI
Detects changes from background level, both SS and transient interference.
Disruptive to quiet all BSSs for measure. Quiet_ANPI varies for mobile STAs. Fails for RFI > EDT. 3
d/dt[ANPI]
Detects onset of interference.
Requires continuing measures. Fails for RFI > EDT. 4
d/dt[FER]
Detects onset of interference using FcsErrorCnt and RcdFragCnt
Requires continuing measures. Fails for very low FERs. 5
STA_ANPI AP_ANPI
STA
Detects local interference at a STA compared to AP baseline.
Requires updates of AP baseline at STA. Fails for RFI > EDT. 6
STA_ChanLoad AP_ChanLoad
Requires updates of AP baseline at STA. Fails for RFI < EDT. 7
d [AP ChanLoad] dt [ BSS_Thruput] AP
Detects SS and transient RFI.
Requires continuing measures. Need BSS_Thruput measure. Fails for RFI < EDT.
Joe Kwak( InterDigital), Jokela, Durand
Submission

7. Simplified d/dt Processing
Rate of change measurand computed as ratio of A/B where:
A is most recent measurand value
B is moving average value of same measurand with specified decay constant
FER is computed using existing MAC counters, FER is ratio of A/B where:
A is (FCSErrorCountn- FCSErrorCountn-1) or (QosRetriesReceivedCount n- QosRetriesReceivedCount n-1)
B is (ReceivedFragmentCount n- ReceivedFragmentCount n-1) or (QosReceivedFragmentCount n- QosReceivedFragmentCount n-1)
BSSThruput needs new definition using received MPDU size and received data rate.
Joe Kwak( InterDigital), Jokela, Durand
Submission

8. Framework for RFI Reporting
Create new Diagnostic Management Alert for RFI detection, similar to Multicast Diagnostic Request/Report.
Triggered Interference Request/Report would permit requestor to:
Select RFI Measurand
Select measurement duration and interval
Select trigger thresholds
Select reporting period
Once requested, RFI detection runs continuously until cancelled.
One Request for each measurand may run concurrently.
Joe Kwak( InterDigital), Jokela, Durand
Submission

9. Element Format Outline
Triggered Interference Request element contains:
Measurand ID
UP (optional, for QOS APs)
Measurement Duration
Measurement Interval (time between measurements)
Aging Window (optional, for d/dt measurands)
Trigger threshold
AP baseline measurement (optional, for baseline measurands)
Reporting period
Triggered Interference Report element contains only the Measurand value.
Dialog tokens match report to request.
Joe Kwak( InterDigital), Jokela, Durand
Submission

10. What Happens Upon RFI Alert?
Like other Measurement and Management tools, out of scope for specification.
Possible AP actions upon receipt:
Determine scope of interference (more measurements)
Decrease data rates
Increase Tx powers
Limit BSS rate sets
Limit new admissions
Consider channel switch
Consider load shedding
Joe Kwak( InterDigital), Jokela, Durand
Submission

11. Joe Kwak( InterDigital), Jokela, Durand
Conclusions
Interference detection using multiple simple measurands is practical and easy to implement.
External interference measurement complements the TGv internal interference diagnostic.
Table of measurands designed to allow growth as new detection techniques emerge.
As WIFI uptake continues, and as unlicensed applications proliferate, RFI detection becomes increasingly important for WLAN performance.
If supported, draft normative text will be presented at next meeting.
Triggered Interference Request/Report satisfies real need and complements existing TGv/TGk measurements.
Joe Kwak( InterDigital), Jokela, Durand
Submission

12. Joe Kwak( InterDigital), Jokela, Durand
STRAW POLL
Do you support use of Triggered Interference Request/Report?
YES _______
NO _______
ABSTAIN _______
Joe Kwak( InterDigital), Jokela, Durand
Submission

13. Joe Kwak( InterDigital), Jokela, Durand
Submission