A method for bidirectional data transmission, preferably in narrowband systems, between a base station and a terminal device includes providing the terminal device and the base station with frequency reference units and transmitting data between the base station and the terminal device over different frequencies. A basic transmit frequency is defined for transmitting data from terminal device to base station, the terminal device defines a terminal device transmit frequency on the terminal device side for transmitting data from terminal device to base station, a frequency offset Δfoffset exists between the basic transmit frequency and the terminal device transmit frequency, the terminal device opens a receive window for data from the base station, and the frequency offset Δfoffset is taken into account for opening the window. Base station determines the terminal device transmit frequency and base station transmits data to terminal device based on the determined terminal device transmit frequency.