Doppler diversity in MC-CDMA using the slepian basis expansion model

Time-variant frequency-selective channels offer multipath diversity and Doppler diversity. MC-CDMA is able to exploit both sources of diversity, if a code with interleaving over the duration of a data block is applied and accurate channel state information is available at the receiver. A time-variant channel equalization scheme based on the Slepian basis expansion model (BEM) and a closely related pilot based channel estimation scheme based on the finite Slepian BEM was proposed by the authors in previous papers. The Slepian BEMs offer significantly reduced bias compared to the well known Fourier BEM. Exploiting the dimensionality of the Slepian BEM we propose an upper bound for the Doppler diversity of a time-variant channel. We present simulation results for a MC-CDMA forward link using an enhanced simulation model for time-variant channels with Jakes' Doppler spectrum. Applying the finite Slepian BEM for channel estimation we are able to take advantage of the additional Doppler diversity offered by a time-variant channel. In other words, the receiver performs better with increasing speed of the user.