GPS Re-Radiator Issues

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GPS Re-Radiator Issues

• Dr. A.J. Van Dierendonck
• AJ Systems
• For the US GPS Industry Council

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Topics

• Comments on commercial applications of Section
  8.3.28 of NTIA Manual of Regulations and
  Procedures for Federal Frequency Management
• Suggested Regulatory Categories
• Possible Licensing Criteria for Commercial
  Entities

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Comments on Section 8.3.28

• Section 8.3.28 provides US agencies and their
  contractors adequate means of using re-radiators
  in furtherance of USG requirements
• NTIA/IRAC rules and FCC experimental licensing
  achieves this goal
• Additional considerations are needed when
  authorizing commercial entities to operate GPS
  re-radiators

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Proposed Regulatory Categories of Commercial Use
of GPS Re-Radiators
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Regulatory Category I

• Category I Commercial Entities Having
  Controlled Public Access
• E.g., GPS industrial operations, universities,
  research institutes
• Operate re-radiators for test purposes
• In facilities having controlled public access
• Within a pre-determined zone to ensure no
  degradation of the public use of GPS
• FCC Part 5 experimental licenses only

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Regulatory Category II

• Other commercial entities
• Do not operate re-radiators for test purposes
• Entities that are open to the public
• Within a pre-determined zone that requires
  additional mitigation to ensure no degradation to
  the public use of GPS
• Can this category be authorized?
• If mobile public use of GPS can be protected,
  then only as a Part 5 experimental authorization
• The Council is working with the re-radiator
  community on possible approaches to the licensing
  of this type of use
• At this time, however, the Council does not see
  how to adequately protect mobile GPS users in
  open access facilities from this category of
  re-radiators

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Issues for Consideration when Licensing
Commercial Entities
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Impact of GPS Re-Radiators on GPS Users

• GPS Re-Radiators do not cause classical noise
  interference
• Except maybe in a rare case
• GPS Re-Radiators can cause multipath errors in
  non-participating GPS Receivers
• If re-radiator is not adequately controlled
• If the environment is not adequately controlled
• If power levels are not controlled, GPS
  re-radiators could cause loss-of-lock and capture
  GPS Receiver tracking loops

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User Receiver Multipath Error Envelope (0.5 Chip
Spacing)
Re-radiated signal amplitude one-half direct
signal amplitude in example Error proportional
to ratio of amplitudes Multipath delay
Re-Radiator signal delay relative to direct signal
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Re-Radiator/Non-Participating GPS User
Operational Environment
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Potential Impact on Non-Participating GPS Users
fromRe-radiators in an Uncontrolled Environment

• E.g., using -140 dBm Re-Radiated Signal _at_ 100
  Feet
• Multipath error based upon error envelope

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Potential Impact (contd)

• Error is proportional to ratio (?) of re-radiated
  signal amplitude to desired signal amplitude
• Based upon nominal desired signal (-125 dBm), ?
  0.178, so reduce error in chart by 0.178/0.5
  0.356
• Total re-radiated signal delay ? 300 feet (0.3
  C/A chips ? 0.3 microseconds)
• Results in an envelope error on the order of ? 50
  feet
• This is a significant error that could occur in
  an uncontrolled environment

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Proposed Commercial License Criteria for Category
I

• FCC Part 5 Experimental License Application to
  include engineering analysis that can be used to
  evaluate impact on non-participating GPS users
• Variables include re-radiated signal power, range
  to possible GPS user, re-radiated signal delay at
  GPS user and, possibly, any re-radiated signal
  attenuation, natural or added
• Multipath errors can then be evaluated and above
  variables could be modified until errors are
  below a specified level
• If error criteria can be met with a reasonable
  re-radiator/GPS user environment, license could
  be granted