On the sensitivity of Zero-tail DFT-spread-OFDM to small bandwidth allocations

The benefits of zero-tail discrete Fourier transform-spread-orthogonal frequency division multiplexing (ZT DFT-s-OFDM) in terms of spectral containment and link performance subsume that the internal guard period of the waveform has negligible power. However, the effective power of such guard period depends in practice on the bandwidth allocation and is still significant in case of small bands. In this letter, we characterize the residual energy of the ZT DFT-s-OFDM guard period and evaluate its impact on spectral containment, non-cyclic inter-symbol interference (ISI) and link performance when small transmission bands are used. Spectral containment is shown not to be affected thanks to the oscillating part of the guard period, which ensures the presence of low power samples in the transition between adjacent time symbols. Despite the larger tail power, link performance is shown to be only marginally affected. This is because small bandwidth configurations experience a nearly flat fading, and therefore minimum non-cyclic ISI over the next symbol.