2001 UPDATE

It is February 10, 2001, seven years after I wrote the little paper titled:

"A DATA LINK FOR COLLISION AVOIDANCE, PRECISION LANDING APPROACHES, AND COMMUNICATION"

Let me clarify and update some items.

SURVEILLANCE:
Several have pointed out that the title does not include the word "surveillance".

The FAA refers to a GPS based ATC system as: "Automatic Dependent Surveillance Broadcast (ADS-B)". http://www.faa.gov/and/and300/datalink/navsur/adsb.htm#0005

The sole purpose of ATC is the prevention of aircraft collisions. In my mind, the term "Collision Avoidance" represents a superset of all the elements of Air Traffic Control. This includes surveillance by controllers on the ground and airborne traffic depiction that would allow "free flight", a term that has come into vogue within the FAA.  http://gps.faa.gov/GPS_FAQs/Free_Flight/free_flight.htm
 

THE PRESENT SYSTEM:
The 1994 paper states: "The present system is over-burdened and inherently error prone."  Seven years later, the situation has not improved.  Not a week goes by without a major event; near misses, system breakdowns causing massive delays and dangerous rerouting of traffic, runway incursion accidents, and routine delays, delays, delays.

COST:
The paper mentioned $300 OEM GPS receivers from Motorola and Rockwell. Such receivers now are in the $50 area, measure a little over one square inch, consume less than one Watt, and exhibit outstanding performance.

SELECTIVE AVAILABILITY:
The paper flirted with the idea that SA, the intentional degradation of GPS accuracy, might be turned off.  On May 1, 2000, it was turned off.

CHECK SUM:
Appendix B assigns 2 packet bytes to a check sum.  It only takes one.

SIMPLICITY:
Above all, simplicity should rule.  While, I have no doubt that the proposed simple modulation scheme and packet definition will work, they are examples only, and certainly do not represent an optimum. Refinement is in order.

However, I worry that complexity and costs will creep in, producing a system suitable only for the air carrier fleet. I worry that it will involve additional satellites, ground stations, and monster software systems that will miss design objectives and fail with regularity.  The system providers  will profit but the tax payer and flying public will lose.  It is history that makes me worry so.

Simplicity, simplicity, and simplicity.

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