###### Abstract
Reference [25] highlighted the integration of THz-enabled UAVs in future 6G networks to enhance data rate, reliability, and resiliency, addressing challenges like trajectory design and channel allocation through a novel distributed safe multi-agent deep reinforcement learning approach. Reference [26] combined the RIS with UAV-based THz mobile networks and optimizes the IRSs' phase shifts, UAVs' trajectories, and system resources to minimize the UAV energy consumption. Reference [27] optimized the multi-layer UAV networks using the THz frequency band to meet the high network demands of delay-sensitive applications in remote areas. Reference [21] discussed the UAV-assisted computation offloading in the THz band to enhance the capabilities of multi-access edge computing for latency-sensitive applications. Reference [28] explored the integration of mmWave, FSO, and THz technologies to enhance data collection capabilities from remote locations through a wireless backhaul link. Reference [29] detailed the application of THz communication in UAV systems, supported by an active reconfigurable intelligent surface (RIS) for enhancing connectivity and reducing interference. Reference [30] utilized advanced distribution models to enhance secure multi-user connectivity for RIS-assisted mixed RF and FSO communications. Reference [31] highlighted the advancement of THz-enabled UAV communications for next-generation networks, focusing on a novel approach that maximizes throughput for ground users through joint optimization of bandwidth, power allocation, and UAV deployment using a non-orthogonal multiple access scheme. To better support computation-intensive applications, it is necessary to reduce the transmission delay from BS to THz-based UAV servers. Advanced modulation schemes and signal processing techniques can improve transmission rates and thus reduce the transmission delay [32]. There have been several studies exploring THz modulation strategies, but each of them has its own limitations. The references [33; 34] proposed a time-spread on-off keying (TSOOK) modulation scheme motivated by the constraint that designing a continuous-wave THz hardware is simply challenging. However, THz-OOK works well only for shorter distances primarily due to the limited Tx power and antenna gains. Moreover, the considered pulse occupies 10 GHz of BW, resulting in huge thermal noise at the receiver. Also, the pulse-based modulation scheme proposed in [35; 36] does not do that well in long-range in the presence of multipath due to the inter-symbol interference (ISI). In order to address this limitation, in [37], the novel distance-aware modulation scheme (DAMC) was presented, which enables the utilization of longer-range links. It permits adaptive transmissions of different symbols on non-overlapping and equally spaced sub-windows in parallel. However, the spectral efficiency of this scheme is low due to the non-overlapped and fixed sub-windows. To improve the spectrum efficiency, the conventional modulation schemes such as orthogonal frequency division multiplexing (OFDM) and discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM), were proposed in the THz regime [38; 39]. However, they are not robust to fast time-varying channels with high Doppler spread, resulting in inter-carrier interference (ICI) and degrading the link performance severely, including data rate and bit error rate (BER) [39]. In [40], the authors proposed the distance-adaptive absorption peak modulation (DA-APM), but it is only valid for covert communications due to adopting the frequencies at the peak path loss. Spatial modulation has also been proposed for THz communications [41; 42], but this modulation strategy results in a high error rate in THz communications. Recently, a new modulation technique named orthogonal time frequency space (OTFS) was proposed to address high Doppler spread in doubly selective channels [43; 44].