Band 255 is a supplemental downlink (SDL) band, used for downlink-only carrier aggregation in the 5 GHz U-NII-3 band. Supplemental DL bands 252 and 255 have been included as part of the LTE-U / LTE-LAA expansion into unlicensed 5 GHz bands U-NII-1 and U-NII-3, respectively.

LTE-U and LTE-LAA implement carrier sensing (CSAT and LBT respectively) to minimise interference with 5 GHz WiFi hardware.