Interfacing according to a common public radio interface in a base station in a mobile communication system is described. The interfacing comprises a conversion process for rate-converting legacy data samples. First a predetermined number of the legacy data samples is converted to frequency samples in a frequency domain, then the frequency samples are zero padded to extend the frequency range according to a related sample rate of a 4G data format and then converted into a number of data samples of the related sample rate. The related sample rate is a multiplication of S/K times a basic frame rate of the 4G data format, S samples being allocated to K frames, K and S being integers and K being 8 or less. Advantageously large buffers for allocating a large number of legacy samples to 4G frames are avoided.