Performance of frequency and time domain coded OFDM over fast fading LEO channels

The orthogonality loss described by intersymbol interference (ISI) and interchannel interference (ICI) when using an OFDM system over LEO satellite channels has been discussed. Major causes of the loss, such as significant Doppler frequency offset, fast fading distortions during OFDM symbols and multipath delays have been studied. The models put up for analyzing are based on their continuous waveforms, using the summation of sine and cosine series. The results obtained give a clear picture of how and to what degree these distortions could affect the useful OFDM symbols. A stochastic model has been developed for modeling the time-varying behavior of the received OFDM signal. Different frequency and time domain coding schemes as well as combined frequency-time domain coding (two-dimensional coding) scheme have been examined. Simulation results have shown that coding in the frequency domain gives a better performance in the slow multipath fading LEO channel, while coding in the time domain is more suitable in the fast fading LEO channel. Combined frequency-time domain coding which has the same complexity as the other two schemes is not suitable for the LEO channel.