GPS ReRadiator Issues Dr A J Van Dierendonck

GPS Re-Radiator Issues Dr. A. J. Van Dierendonck AJ Systems For the US GPS Industry Council 10 -28 -2005 GPS Re-Radiators 1

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 10 -28 -2005 GPS Re-Radiators 2

Comments on Section 8. 3. 28 provides US agencies and their contractors adequate means of using reradiators 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 10 -28 -2005 GPS Re-Radiators 3

Proposed Regulatory Categories of Commercial Use of GPS Re-Radiators 10 -28 -2005 GPS Re-Radiators 4

Regulatory 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 10 -28 -2005 GPS Re-Radiators 5

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 10 -28 -2005 GPS Re-Radiators 6

Issues for Consideration when Licensing Commercial Entities 10 -28 -2005 GPS Re-Radiators 7

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 10 -28 -2005 GPS Re-Radiators 8

User Receiver Multipath Error Envelope (± 0. 5 Chip Spacing) Re-radiated signal amplitude = onehalf direct signal amplitude in example Error proportional to ratio of amplitudes Multipath delay = Re -Radiator signal delay relative to direct signal 10 -28 -2005 GPS Re-Radiators 9

Re-Radiator/Non-Participating GPS User Operational Environment 10 -28 -2005 GPS Re-Radiators 10

Potential Impact on Non. Participating GPS Users from Re-radiators in an Uncontrolled Environment E. g. , using -140 d. Bm Re-Radiated Signal @ 100 Feet Multipath error based upon error envelope 10 -28 -2005 GPS Re-Radiators 11

Potential Impact … (cont’d) Error is proportional to ratio ( ) of re-radiated signal amplitude to desired signal amplitude • Based upon nominal desired signal (-125 d. Bm), = 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 10 -28 -2005 GPS Re-Radiators 12

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 reradiator/GPS user environment, license could be granted 10 -28 -2005 GPS Re-Radiators 13