A bandwidth that is allocated to a transmitted waveform need not be contiguous in frequency space and a frequency content of the transmitted waveform may vary, as needed, even on a signaling interval by signaling interval basis, in order to accommodate a desired transfer rate, reduce or avoid interference and/or enhance an end user experience. According to embodiments of the invention, a set of frequencies that is used to provide frequency content to elements of a waveform alphabet, used to form the transmitted waveform, is varied thus varying a frequency content of the transmitted waveform. A time span associated with the elements of the waveform alphabet may also be varied. Various transmitter/receiver embodiments are disclosed including direct synthesis transmitter/receiver embodiments.