# Enhancing PAPR and Throughput for DFT-s-OFDM System Using FTN and IOTA Filtering
## 1 Introduction  
High frequency, i.e., millimeter wave (mmWave) and terahertz (THz) wireless communication technology, which exploits the treasure of large bandwidth in higher frequency, has become a research hotspot with the evolution of B5G and 6G [1, 2, 3, 4]. The aim of high frequency technology is to provide extremely high-speed data rate for various applications, such as vehicular networks, satellite backhauls, extended reality (XR) applications, etc. [5, 6, 7, 8, 9, 10]. The characteristics of the devices and the propagation environment are significantly different at high frequency. For example, the linear range of the amplifier at high frequency is small, which causes unexpected distortion on the signal waveforms with a large variance [11]. The design of the waveform thus becomes a major concern in enabling high frequency communication. The designs of waveforms based on orthogonal frequency division multiplexing (OFDM) have been commercialized in 4G/5G, and are now the baseline of 6G high frequency communication [12, 13]. Parallel transmission of high speed data is realized in OFDM through time and frequency division multiplexing, which has good resistance to multi-path fading and can support efficient multi-user access. Discrete Fourier transform (DFT) spreading technique has been incorporated in OFDM, termed DFT-s-OFDM, to achieve lower peak-to-average power ratio (PAPR) so as to make it compatible with the low-ability power amplifier, e.g., cellular uplink and ground-to-satellite link. While maintaining the characteristics of single-carrier waveforms, DFT-s-OFDM offers more flexibility compared to the conventional single-carrier system. DFT-s-OFDM has been applied in high frequency communication scenarios [14], which realize multi-user multiplexing whenensuring good PAPR performance. It has also been proved that DFT-s-OFDM can achieve a balance between user scheduling flexibility and computational complexity of channel equalization [15], which enables usage in wireless hotspots with densely distributed user equipment. Recently, waveform variants based on DFT-s-OFDM, e.g., generalized DFT-s-OFDM which redesigns the cyclic prefix (CP) [16; 17], have triggered more research interest in achieving lower latency and out-of-band emission. Despite the above variances, achieving the improvement of both the PAPR and throughput at the same time is a challenge. To enhance the spectral efficiency, utilizing high-order modulation is a straightforward method. However, the different amplitudes of modulated symbols leads to larger PAPR, which makes reducing PAPR and enhancing throughput contradictory. As for the methods which achieve lower PAPR, e.g., applying DFT spreading on OFDM, they cannot improve the spectral efficiency. PAPR can be further lowered by methods such as peak clipping. However, this can cause signal distortion and the spectral efficiency is sacrificed. FTN signaling is an efficient method for enhancing the spectral efficiency, with the disadvantage of low transmission reliability due to the additional ISI brought by acceleration. In order to further enhance the spectral efficiency of transmission, faster-than-Nyquist (FTN) technology has been put forward and introduced into some existing waveform frameworks. Compared to the systems based on Nyquist criteria, FTN signaling can achieve 25% improvement in symbol rate without sacrificing the error rate performance. Basic ideas of incorporating FTN signaling in OFDM-based waveforms are introduced in [18]. FTN also exhibits high compatibility with different modulations, where [19] validates the capacity and SNR gain of FTN-based low-order modulations, and [20] proves the power gains of FTN-based high-order modulations in a multi-carrier system. As for the receiving technology of FTN, [PERSON]. [21] investigates the maximum posterior-based detection of FTN signaling, which achieves up to 186% gains in spectral efficiency compared with its counterpart of Nyquist signaling. To reduce the computational complexity of the FTN receiver, [PERSON].