ES.3.2 WAAS/LAAS
The following GPS/WAAS actions should also be taken to support development of a national GPS plan：
a. Establish the size and characteristics of the GEOS constellation that will be maintained to support civil aviation requirements. The plan will allow for the WAAS configuration to sensibly evolve and adapt in response to the availability of GPS satellite improvements. This study concluded that four GEOS are required to augment the current GPS satellite capabilities.
b. Further analyze, design, and validate the ionospheric correction methodology to support sizing of the ground reference station requirements and mitigation of the ionospheric risks discussed previously. Analyze possible robust receiver designs for mitigation of scintillation effects. Validate both analyses using National Satellite Test Bed(NTSB) and Phase 1 WRS data.
ES.3.3 INTERFERENCE RISKS
The following recommendations are directed at system risks.
a. Develop regulations for all licensed transmitters that explicitly limit radio frequency (RF) emissions at satellite radio-navigation frequencies.
b. Require compliance monitoring of potential sources of satellite radio-navigation interference after maintenance or new construction.
c. Ensure that interference levels at satellite radio-navigation frequencies are measured during flight inspections at airports where GPS approaches are planned and where a potential unintentional interference threat exists.
d. Derive a DOT-authorized threat definition to support design of mitigation actions for intentional GPS signal interference.
e. Implement enforcement measures to discourage and remedy potential threats. Threat detection might be part of standard user aircraft reporting structure, but a separate airborne platform will be needed to locate the threat (s). This activity should naturally be coordinated with law enforcement agencies.
f. Develop traffic control procedures and provide training to overcome wide-area GPS signal outage caused by intentional interference.
g. Develop standards for onboard interference suppression system performance that address postulated threat (s), aircraft types, and postulated traffic control procedures.
h. Obtain measurements of underbody aircraft antenna gain and assess advantages of antenna locations to determine antenna pattern benefits.
i. Evaluate additional means for aircraft-based interference suppression. These might include antenna nulling and signal processing techniques and integration with inertial navigation instrumentation.
j. Review the risk of interference from military OTH radar.
