Training Design for CFO Estimation in OFDM Over Correlated Multipath Fading Channels

Carrier frequency offset (CFO) estimation is a key challenge in multicarrier systems such as OFDM. Often, this task is carried out using a preamble made of a number, say J, of repetitive-slots (RS). Here, we address the issue of optimal RS preamble design using the Cramer -Rao bound. We show that the optimal value of J is a trade-off between the multipath diversity gain and the number of unknowns to be estimated. In the case of correlated channel taps, we show that uniform power loading of the active subcarriers is not optimal (in contrast with the uncorrelated case) and a better power loading scheme is proposed. The theoretical results are supported by computer simulations.