Frequency Spectrum Rotation in Interleaved Frequency Division Multiplexing

Interleaved frequency division multiplexing (IFDM) can achieve high diversity gain as well as can establish orthogonal frequency multiplexing by means of comb-shaped frequency spectrum. In IFDM, as the number of multiplexing users becomes large, the comb-shaped frequency spectrum should be narrow, so that frequency diversity gain is decreased. In addition, IFDM suffers from inter-path interference introduced in the transmitted signal by multipath fading channel. In this paper, the frequency spectrum rotation is proposed. In the proposed method, the comb-shaped frequency spectrum is frequency-shifted for every modulated symbol. As a result, the frequency spectrum of the frame composed of many modulated symbols is widely spread. In addition, the inter-path interference can be suppressed because the modulated symbol is orthogonal in frequency with its time-consecutive symbol. From the computer simulation, the frequency rotation can achieve the better error rate performance thanks to increasing frequency diversity gain and suppressing inter-path interference.