Two key challenges in the design of datalinks for unmanned aircraft (UAS) systems compared to other wireless links are the long range of distances and speeds that need to be covered. The 960 - 1164 MHz part of the IEEE L band has been identified as a candidate spectrum for future manned and unmanned aircraft datalinks. The amount of spectrum available in the L-Band is not sufficient to support video applications common in UASs and so dual-band designs using both L-Band and C-Band are being considered. For L-Band, two projects funded by EUROCONTROL L-Band Digital Aeronautical Communications Systems 1 and 2 (L-DACS1 and L-DACS2) are often mentioned for use in UAS also. We briefly discuss issues with their use for UAS. We compare the two proposals in terms of their scalability, spectral efficiency, and interference resistance. Then we discuss several issues in UAS datalink design including availability, networking, preemption, and chaining. We also propose ways to mitigate interference with other systems in the L-Band.
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