On the impact of the pilot density in the channel estimation of MC-CDMA systems

In this paper we investigate the impact of the pilot density (and associated pilot distances for both frequency and time domains) in the performance of the channel estimation for MC-CDMA systems, when using dedicated sub-carriers to transmit pilots with 2-D rectangular patterns. The analytical formulation of the channel estimation MSE for the single-user downlink scenario with a generic channel estimation scheme for a given power efficiency is presented. The attained results go beyond the commonly accepted rule of thumb that suggests that an oversampling factor of two will result in a good trade-off between performance and pilot overhead. The analytical formulation was validated by system simulations. A scenario using the 2-D LS-DFT channel estimation scheme confirmed the analytical result. The lowest channel estimation MSE for a given value of power efficiency is achieved when the pilot density is the one that closely fulfils the 2-D sampling theorem.