In order to maintain flexible system bandwidth and a flexible center frequency, without requiring a cyclic prefix or guard interval, a transmitter apparatus transmits a reference signal based on a single carrier waveform having a mixed symbol structure, in reference signal symbols using at least one of a cyclic prefix and a guard interval and transmits data based on the single carrier waveform without the cyclic prefix or the guard interval. The data may be based on input data processed using overlapping FFT windows, and an amount of overlap between the FFT windows may be configurable by the transmitter or the receiver. An apparatus receiving the downlink transmission comprising data based on a single carrier waveform may process the data based on overlapping FFT windows.