Digital air/ground communications for air traffic control

A system which provides four voice of data channels per 25-kHz frequency channel by utilizing time division multiple access (TDMA) technology is described. Ground and airborne channel users are assigned separate uplink and downlink frequencies. This provides the greatest opportunity for efficient RF spectrum utilization through frequency reuse over an extended volume of airspace. The introduction of integral data with voice to a common channel allocation provides a mechanism to reduce voice traffic and controller/pilot work load for frequency changes. The digitizer chosen for quantization of the analog voice was selected for its high intelligibility in moderate to high bit-error-rate environments while preserving speech quality. A prototype of the system was designed and fabricated to assist in the evaluation of the tradeoffs between the system capabilities, overall implementation complexities, and resulting costs