Bandwidth efficient techniques for helicopter links via satellite

Helicopter radio links via satellite are limited in performance when the antenna is located below the main rotor. The fuselage may obstruct the line-of-sight signal and the rotating blades not only periodically block it but also generate reflections which cause periodic ripples in the signal complex envelope. This paper presents receive diversity and transmit space time coding with up to three antennas combined with variable high order modulation and coding techniques in order to overcome these problems allowing unprecedented bandwidth efficiencies in helicopter links for existing and future satellite systems. As a satellite system example, the Inmarsat enhanced Broadband Global Access Network (BGAN) is considered operating over the Alphasat satellite to be launched in 2013 over the European airspace by Inmarsat and ESA. With the proposed techniques and radio upgrades, bandwidth efficiency approaching 5 b/s/Hz may be achievable to/from helicopters and at the same time the reliability of the link and service area increases.