where formula_61 is the formula_62th polyphase component of the channel formula_63. From (1), one can see that the original ISI channel is converted to formula_43 many vector subchannels of vector size formula_38. There is no ISI across these vector subchannels but there is ISI inside each vector subchannel. In each vector subchannel, at most formula_66 many symbols are interfered each other. Clearly, when the vector size formula_67, the above VOFDM returns to OFDM and when formula_68 and formula_69, it becomes the SC-FDE. The vector size formula_38 is a parameter that one can choose freely and properly in practice and controls the ISI level. There may be a tradeoff between vector size formula_38, demodulation complexity at the receiver, and FFT size, for a given channel bandwidth.