To improve the spectral efficiency of the 5th generation mobile communication system (5G) and beyond, the universal time-domain windowed orthogonal frequency division multiplexing (UTW-OFDM) has been proposed. Particularly, the simplified UTW-OFDM is highly compatible with the conventional cyclic-prefix-based OFDM (CP-OFDM). It can strongly suppress out-of-band emission (OOBE) with a simple configuration of multiplying a time window with a long transition length. However, in the simplified UTW-OFDM, multiplication of the time window causes inter-carrier interference (ICI), which degrades the communication quality, especially for higher-order modulation schemes such as 64QAM. In this paper, firstly, we investigate the applicability of the simplified UTW-OFDM to 5G. Next, an ICI canceller is proposed for the simplified UTW-OFDM-applied 5G system to improve the communication quality. In the proposed method, an optimal ICI cancellation weight is designed by taking the noise enhancement suppression into account. The proposed method improves communication quality while achieving stronger OOBE suppression. In the case of 64QAM, the simplified UTW-OFDM can suppress the PSD at the channel edge by up to 45.0 dB compared to that of CP-OFDM.