Date Added: Jul 2011
The authors consider the impact of Doppler frequency shift on the Orthogonal Frequency Division Multiple Access (OFDMA) signal and Frequency Bank Signal (FBS) transmitted over High Altitude Platforms (HAPs). Theoretical analysis and simulations show that OFDMA systems perform well when the Doppler frequency shift is smaller than 2% of carrier frequency separation. These conditions correspond to operation frequency of 2GHz and train velocities up to 120 km/h. FBS method, on the other hand, allows working under more severe Doppler effects, namely a Doppler shift of up to 6 - 8 %, hence enabling higher carrier frequency bands and higher vehicle speeds.