A signal decoder in a communication system is for decoding signal elements in a communication signal having interleaved carrier frequencies. The decoder receives antenna signals in a frequency domain, and has a multiplier for multiplying the antenna signals by a complex-valued mathematical sequence such as the Zadoff-Chu sequence, to generate multiplied antenna signals. An inverse frequency to time converter converts the multiplied antenna signals to time domain signals. A signal quality detector detects a signal quality from the time domain signals based on a subset of the carrier frequencies. The complex-valued mathematical sequence is provided with zero values corresponding to carrier frequencies that are not included in the subset, and the inverse frequency to time converter has a transform size corresponding to the multiplied antenna signals including all carrier frequencies.