Interference

1
800 MHz REBANDINGEnhanced Best Practices
GuideAnd Interference Protection
Part 4 in the APCO 800 ALERT Webinar Series
January 19, 2005 David Buchanan, County of San
Bernardino, CA Glen S. Nash, State of California
DGS Communications Ron Haraseth, APCO-AFC, Inc.
2
The Near-Far Problem

• This interference is an example of the Near - Far
  Problem
• Public Safety desired signals from a distant site
  are relatively weaker than the strong signals
  from a nearby Cell Site
• The cell site operates in compliance with FCC
  rules

3
Best Practices Guide

• April 2000 FCC calls group together
• APCO
• Nextel
• CTIA
• PSWN
• December 2000 Groups presents BPG to the FCC

4
The Cause

• Out of Band Emissions (OOBE)
• Transmit noise from the cell site
• Appears as an on channel signal to the receiver
• Receiver Intermodulation
• Non-Linear mixing of the cell site transmit
  carriers in the receiver front end
• Portables most susceptible to Receiver
  Intermodulation

5
Location of Spectrum
Intermodulation - Mathematics
2A-BC
806
809.75
821
816
824
NPSPAC (Public Safety)
Cellular A B gtgtgtgtgtgtgt
General Category
Interleaved Spectrum
ESMR (Upper 200)
851
854.75
866
861
869
AB-CD 2ABC Third Order Intermod
2A-BC
6
Why the Interference Can be Hard to Identify

• Interference potential in limited, but specific
  areas.

Computer generated simulated propagation for
typical public safety system showing potential
areas of interference.
7
Intermittent InterferenceA Concurrence of Events
Time and Location
User in Problem Area Public Safety Radio in
Use Interfering Radio A Transmits Interfering
Radio B Transmits Harmful Interference Results
TIME
When all four elements concurrently active
8
What to Do

• There are no sure ways to eliminate the
  interference
• Until the re-band is complete
• Retune cell channels further away from public
  safety channels Add band pass filters to cell
  site transmitters to reduce OOBE
• Change cell site transmit power, antenna type and
  height
• Increase public safety receive levels

9
Enhanced Best Practices

• REPORT AND ORDER, FIFTH REPORT AND ORDER, FOURTH
  MEMORANDUM OPINION AND ORDER, AND ORDER (FCC
  04-168)
• Appendix D - Enhanced Best Practices
• http//hraunfoss.fcc.gov/edocs_public/attachmatch/
  FCC-04-168A1.doc

10
Reporting Interference

• Central registry
• Joint responsibility of the commercial carriers
  to create and maintain
• Common electronic means
• Information to include
• the specific geographical location where the
  interference occurs, and the time or times at
  which the interference occurred or is occurring
• a description of the scope and severity of the
  interference
• the source of the interference if known
• the relevant FCC licensing information of the
  party suffering the interference and
• a single point of contact for the party suffering
  the interference

11
Your Rights

• Cellular providers must respond to within 24
  hours when you report interference
• Report Location, time, description of
  interference, the source if known,the licensees
  license information and where you can be
  contacted
• There will be a single common electronic means to
  report interference
• You and the cellular companies must act in good
  faith

12
Your Rights

• Pre-reconfiguration - If your median signal
  level is equal or greater than 85 dbm for
  portables or 88 dBm for mobiles the cellular
  companies must fix any interference
• If your levels are less than above Cellular
  companies must mitigate interference to up to
  four control channels
• Cellular companies must exercise best efforts to
  mitigate public safety interference on the public
  safety systems voice channels
• If they cannot mitigate voice channel
  interference they must provide report detailing
  the reasons
• The TA mediates any disputes

13
Your Rights

• Post reconfiguration any interference must be
  mitigated if your median minimum signal levels
  are 101 dBm for portables and 104 dBm for
  mobiles.
• The response times remain at 24 hours
• Note these protections are modified if your
  channel is between 861and 862 MHz

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Where can I get more information?

• Resources
• News
• Presentations, Webinars, Symposiums
• Documents
• Links to manufactures 800 support sites
• Links to other support sites

• WWW.800MHZ.ORG

15
THANK YOU

• APCO 800 ALERT
• Resources
• Links
• Question/Answers
• Email contact for Questions or Comments
  800alert_at_apco911.org
• WWW.800MHZ.ORG
• WWW.APCOINTL.ORG