GPS Re-Radiator Issues

1. GPS Re-Radiator Issues Dr. A.J. Van Dierendonck AJ Systems For the US GPS Industry Council GPS Re-Radiators

2. 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 GPS Re-Radiators

3. 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 GPS Re-Radiators

4. Proposed Regulatory Categories of Commercial Use of GPS Re-Radiators GPS Re-Radiators

5. 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 GPS Re-Radiators

6. 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 GPS Re-Radiators

7. Issues for Consideration when Licensing Commercial Entities GPS Re-Radiators

8. 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 GPS Re-Radiators

9. 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 GPS Re-Radiators

10. Re-Radiator/Non-Participating GPS User Operational Environment GPS Re-Radiators

11. Potential Impact on Non-Participating GPS Users fromRe-radiators in an Uncontrolled Environment • E.g., using -140 dBm Re-Radiated Signal @ 100 Feet • Multipath error based upon error envelope GPS Re-Radiators

12. Potential Impact … (cont’d) • 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 GPS Re-Radiators

13. 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 GPS Re-Radiators