A method of transmitting output symbols in sub-slots, each of the sub-slots having a predetermined length, the method comprising: generating, by a user equipment, UE, a first output symbol having a first symbol length that is shorter than the predetermined length; transmitting, by the UE, the first output symbol with a guard period having a guard period length, wherein a sum of the first symbol length and the guard period length is less than or equal to the predetermined length, and wherein no transmission is made by the UE during the guard period; generating, by the UE, a plurality of other output symbols that each have the predetermined length; and immediately following the transmission of the first output symbol, transmitting, by the UE, the plurality of other output symbols; wherein the first output symbol is an IDFT-modulated symbol, and wherein generating the first output symbol comprises: performing a frequency modulation operation on a first set of input symbols, wherein the frequency modulation operation is an inverse Fourier transform that uses a set of consecutive sub-carrier frequencies; generating, with the inverse Fourier transform, a periodic output by interleaving a set of inputs that are all zero among the input symbols, wherein the interleaving comprises assigning non-consecutive sub-carrier frequencies to modulate the input symbols, and comprises assigning sub-carrier frequencies that are between the non-consecutive sub-carrier frequencies to modulate the set of inputs that are all zero; extracting one period of the periodic output; and adding a cyclical prefix to the extracted output, wherein the first output symbol includes only the extracted output with the added cyclical prefix. generating, by a user equipment, UE, a first output symbol having a first symbol length that is shorter than the predetermined length; transmitting, by the UE, the first output symbol with a guard period having a guard period length, wherein a sum of the first symbol length and the guard period length is less than or equal to the predetermined length, and wherein no transmission is made by the UE during the guard period; generating, by the UE, a plurality of other output symbols that each have the predetermined length; and immediately following the transmission of the first output symbol, transmitting, by the UE, the plurality of other output symbols; wherein the first output symbol is an IDFT-modulated symbol, and wherein generating the first output symbol comprises: performing a frequency modulation operation on a first set of input symbols, wherein the frequency modulation operation is an inverse Fourier transform that uses a set of consecutive sub-carrier frequencies; generating, with the inverse Fourier transform, a periodic output by interleaving a set of inputs that are all zero among the input symbols, wherein the interleaving comprises assigning non-consecutive sub-carrier frequencies to modulate the input symbols, and comprises assigning sub-carrier frequencies that are between the non-consecutive sub-carrier frequencies to modulate the set of inputs that are all zero; extracting one period of the periodic output; and adding a cyclical prefix to the extracted output, wherein the first output symbol includes only the extracted output with the added cyclical prefix. performing a frequency modulation operation on a first set of input symbols, wherein the frequency modulation operation is an inverse Fourier transform that uses a set of consecutive sub-carrier frequencies; generating, with the inverse Fourier transform, a periodic output by interleaving a set of inputs that are all zero among the input symbols, wherein the interleaving comprises assigning non-consecutive sub-carrier frequencies to modulate the input symbols, and comprises assigning sub-carrier frequencies that are between the non-consecutive sub-carrier frequencies to modulate the set of inputs that are all zero; extracting one period of the periodic output; and adding a cyclical prefix to the extracted output, wherein the first output symbol includes only the extracted output with the added cyclical prefix.