A method of operating a wireless communication system is disclosed. The method includes receiving first and second parallel data streams. The first data stream is converted to a first frequency-domain data stream by a discrete Fourier transform (DFT) having NDFT0 size, where NDFT0 is a positive integer. The second data stream is converted to a second frequency-domain data stream by a DFT having NDFT1 size, where NDFT1 is a positive integer. The first and second frequency-domain data streams are mapped to respective subcarriers.