Channel Estimation for AF-Type Cooperative OFDM Systems With Low Pilot Overhead

In amplify-and-forward (AF) type relaying assisted orthogonal frequency division multiplexing (OFDM) systems, channel estimation (CE) is a challenging task due to the increased frequency selectivity caused by the cascaded source-to-relay-to-destination $(S\rightarrow R\rightarrow D)$ multipath channel. Typically, such cascaded channels result in severe time dispersion. Consequently, it requires additional pilot overhead for CE as well as longer cyclic prefix (CP) for eliminating the inter-symbol interference (ISI), which will inevitably reduce the achievable diversity provided by cooperative transmissions. In this letter, a three-step CE scheme is proposed without the need of increasing pilot overhead. Furthermore, by reconstructing the CP at the relay node, the CP length does not necessarily need to be extended for the cascaded channel. Simulation results demonstrate the effectiveness of our proposed scheme even in severely time-dispersive multipath fading channels.