Embodiments of the invention provide a receiver in an OFDM based communication system adapted to perform channel estimation using a received reference signal transmitted from at least one antenna, said reference signal being substantially located into two OFDM symbols of a transmission time interval comprising of more than two OFDM symbols. A method of generating pilot structure, the pilot structure provides information to an apparatus for channel estimation in the OFDM system with a transmission time interval of seven OFDM symbols. The pilot structure comprising pilot signals from at least one transmitting antenna located in various OFDM symbols of the transmission time interval.