New air-to-ground wireless datalinks are needed to supplement existing civil aviation technologies. The 960 - 1164 MHz part of the IEEE L band has been identified as a candidate spectrum. EUROCONTROL - the European organization for the Safety of Air Navigation, has funded two parallel projects and developed two proposals called L-DACS1 and L-DACS2. Although, there is a significant amount of literature available on each of the two technologies from the two teams that designed the respective proposals, there is very little independent comparison of the two proposals. The goal of this paper is to provide this comparison. We compare the two proposals in terms of their scalability, spectral efficiency, and interference resistance. Both the technologies have to co-exist with several other aeronautical technologies that use the same L-band. We discuss two coexistence strategies along with an analysis of the performance of the link.
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