A variety of all-new systems such as a massive machine type communication (mMTC) system will be supported in 5G and beyond. Although each mMTC device occupies quite narrow bandwidth, the massive number of devices expected will generate a vast array of traffic and consume enormous spectrum resources. Therefore, it is necessary to proactively gather up and exploit fractional spectrum resources including guard bands that are secured but unused by the existing Long Term Evolution (LTE) systems. The guard band is originally secured as a margin for high out-of-band emission (OOBE) caused by the discontinuity between successive symbols in the cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM), and new-waveforms enabling high OOBE suppression have been widely researched to efficiently allocate narrowband communication to the frequency gap. Time-domain windowing is a well-known signal processing technique for reducing OOBE with low complexity and a universal time-domain windowed OFDM (UTW-OFDM) with a long transition duration exceeding the CP length has demonstrated its ability in WLAN-based systems. In this paper, we apply UTW-OFDM to the LTE downlink system and comprehensively evaluate its performance under the channel models defined by 3GPP. Specifically, we evaluate OOBE reduction and block error rate (BLER) by computer simulation and clarify how far OOBE can be reduced without degrading communication quality. Furthermore, we estimate the implementation complexity of the proposed UTW-OFDM, the conventional CP-OFDM, and the universal filtered-OFDM (UF-OFDM) by calculating the number of required multiplications. These evaluation and estimation results demonstrate that the proposed UTW-OFDM is a practical new-waveform applicable to the 5G and beyond.

In a time-invariant wireless channel, the multipath that exceeds the cyclic prefix (CP) or the guard interval (GI) causes orthogonal frequency division multiplexing (OFDM) systems to hardly achieve high data rate transmission due to the inter-symbol interference (ISI) and the inter-carrier interference (ICI). In this paper the new canceller scheme, named as Double Window Cancellation and Combining (DWCC) is proposed. It includes the entire symbol interval, delayed by multipath as a signal processing window and intends to improve the performance by combining the double windows that can be formed by the pre- and post-ISI cancellation and reconstruction to the received OFDM symbol interfered by the multipath exceeding the guard interval. The proposed scheme has two algorithm structures of the DWCC-I and -II which are distinguished by the operational sequence (Symbol-wise or Group-wise) to the OFDM symbols of the received packet and by the selection of the processing window in the iterative decision feedback processing. Since the performance of the canceller is dependant on the equalization, particularly on the initial equalization, the proposed schemes operate with the time and frequency domain equalizer in the initial and the iterative symbol detection, respectively. For the verification of the proposed schemes, each scheme is evaluated in the turbo coded OFDM for low (QPSK) and high level modulation systems (16QAM, 64QAM), and compared with the conventional canceller with respect to the performance and computational complexity. As a result, the proposed schemes do not have an error floor even for 64QAM in a severe frequency selective channel.

In conventional OFDM systems, the effect of inter-block-interference (IBI) can be completely removed by inserting sufficient redundant symbols between successive transmission blocks. In this paper, based on the reformulated received block symbols of the discrete multirate filterbanks model, a new transceiver model for the cyclic prefix (CP) OFDM systems is proposed, associated with the oblique projector technique (view as the pre-processor for achieving IBI-free). Consequently, a novel ISI-free receiver with the zero-order FIR zero-forcing (ZF) filterbanks equalizer can be devised, under noise-free environment. For performance comparison the bit-error-rate (BER) is investigated for the cases of noisy and noise-free channels. In all cases, viz., the length of CP is shorter or longer than the order of the channel impulse response, we show that the same BER performance compared with the one suggested in [3] can be achieved, under the same assumptions and conditions. Since a simple cascade configuration of the IBI cancellation using the oblique projector followed by the ISI cancellation using the zero-order FIR ZF filterbanks equalizer can be realized for OFDM systems with sufficient or insufficient CP, the complexity of transceiver design can be reduced.