  N-continuous orthogonal frequency division multiplexing (NC-OFDM) is a
promising technique to achieve significant sidelobe suppression of baseband
OFDM signals. However, the high complexity limits its application. Based on
conventional NC-OFDM, in this paper, a new technique, called time-domain
N-continuous OFDM (TD-NC-OFDM), is proposed to transfer the original
frequency-domain processing to the time domain, by the linear combination of a
novel basis set to smooth the consecutive OFDM symbols and their high-order
derivatives. We prove that TD-NC-OFDM is an equivalent to conventional one
while consuming much lower complexity. Furthermore, via the time-domain
structure, a closed-form spectral expression of NC-OFDM signals is derived and
a compact upper bound of sidelobe decaying is derived. This paper also
investigates the impact of the TD-NC-OFDM technique on received
signal-to-interference-plus-noise ratio (SINR) and provides a closed-form
analytical expression. Theoretical analyses and simulation results show that
TD-NC-OFDM can prohibitively suppress the sidelobe with much lower complexity.
