## 5 Conclusions  
In this paper, it is shown that an increase in the throughput of DVB channels, especially in satellite DVB-S2X applications, can be achieved by using optimal FTN signals with compact OQPSK modulation. A method for optimizing the shape of signals having a specified reduction rate of the out-of-band emission level, the minimum ISI level, and the required PAPR of the radiated oscillations is developed. For the first time, the possibility of synthesizing signals with OQPSK is shown, which provides not only high compactness of the spectrum and the required correlation properties but also makes it possible to regulate PAPR. This further provides the possibility of introducing regulation of the average power of a signal packet in the existing DVB-S2X systems, i.e., in devices amplifying oscillations of a satellite repeater using traveling wave tubes or powerful transistors. At the same time, using the proposed optimal FTN signals with OQPSK makes the frequency plan of the data transmission network able to be reduced, and the data transmission rate can be increased when the same frequency mask is used. Optimal FTN signals which can provide PAPR reduction by at most 3 dB were found. These signals also allow obtaining the energy gain up to 2 dB compared to known RRC pulses, while the occupied frequency bandwidth and transmission rate remain constant.  
The simulation results show that the proposed optimal FTN signals with QPSK and OQPSK can be successfully used in channels when there is AWGN or Rayleigh fading since they are analyzed separately. The energy consumption in these channels is close  
Figure 18: BER performance of optimal FTN signals in frequency-flat Rayleigh channel: (**a**) QPSK, and (**b**) OQPSK.  
to the energy consumption of classical OQPSK signals with a rectangular pulse shape in quadrature channels and wide frequency bandwidth. In addition, the adjustment of the average power of a signal packet makes it possible to obtain an energy gain of 2-3 dB while reducing the PAPR of the emitted signals.  
The proposed signal can be used not only in DVB-S2X systems but also in low-rate return channels of interactive broadcasting systems with a frequency resource shortage. In addition, the proposed method paves the way for constructing signals for certain spectral and energy characteristics of transmission channels with a specific frequency mask, taking into account both the requirements for PAPR and the correlation properties of signal packets.  
Funding acquisition and supervision, S.B.M., W.X., and Y.X.; methodology, formal analysis, investigation, and simulation modeling, all authors; optimization problem solving, A.S.O.; writing and original draft preparation, S.B.M., A.S.O., and S.V.Z.; and full paper review and revision, M.L. All authors have read and agreed to the published version of the manuscript.  
The research was funded by the Ministry of Science and Higher Education of the Russian Federation as part of World-class Research Center program: Advanced Digital Technologies (contract No. 075-15-2020-934 dated 17 November 2020), International Science & Technology Cooperation Program of China (2014 DFR10240), the Fundamental Research Funds for the Central Universities (3072020 CF0803), and the Opening Fund of Acoustics Science and Technology Laboratory (Grant No. SSKF2020010).  
The authors declare no conflict of interest.