Purpose

The objectives of this study are, through field testing and analytical analysis, to:

1. validate the use of the free-space path model in link budget calculations;

2. determine the actual link margin values that should be used in the link budget calculations;

3. determine the fading levels which must be accounted for in link budget calculations;

4. determine the maximum GPS radiosonde interference level that can be tolerated by a GPS radiosonde.

Once identified, these values can be used in future compatibility and interference studies.

Calculation of interference criteria is based on both the Metaids system link margin, and the link availability values of the system. There is a need to clearly define the term availability for Metaids systems, and to determine the appropriate link budget to be used with defining Metaids interference criteria.

In the ITU-R, Metaid's system interference criteria are typically based on the system link margin. A percentage of the link margin is given up to interference. The noise floor is raised slightly by the presence of the interference, resulting in a reduction in the link margin. The link availability objectives of the system must also be considered in order to determine the percentages of time that are applicable to the calculated interference criteria. This is the method used for the current values specified in Recommendation ITU-R RS.1263.

In past years, other radio services have noted that the Metaids performance objectives are set very high (link availability on the order of 99%) while the specified link margins are quite low (on the order of several dB or less). Such low link margins are not common radio link design practice and raised concern for the other radio services. However, for technical and safety reasons discussed in Recommendation ITU-R RS.1165, Metaids systems are designed to make the most efficient use of transmitter power and minimize the weight and density of the Metaids transmitter package.