# Gyre Precoding and T-Transformation-Based GFDM System for UAV-Aided mMTC Network
## 1 Introduction  
An uncrewed aircraft handled by remote control or embedded computer programs is commonly known as an unmanned aerial vehicle (UAV) or drone. Recently, there has been tremendous amount of interest growing to develop UAV-ground communications using low-cost massive UAVs under existing 5G as well as future-generation (B5G/6G) cellular networks. To maintain secure and reliable flight operation, UAVs can exchange safety-critical information with remote pilots, closest aerial vehicles, and air traffic controllers with an assistance of control and non-payload communication (CNPC). UAVs are also delivering goods and improving the throughput of 5G networks [1, 2, 3]. Additionally, mission-oriented data, such as high-resolution video, data packets, and aerial images, are possible to seamlessly transfer with UAVs in payload communication. Even in an emergency situation when terrestrial mobile stations go through unexpected discontinuity due to disasters, UAVs can be utilized as a base station (BS) or as a relaystation (RS). Due to flexible deployment and cost effectiveness, full-duplex UAVs can also be integrated with terrestrial cellular networks [4]. A typical scenario is illustrated in Figure 1, where UAVs are forming a cooperative relay network with an assumption that there is no direct connection between BS and user equipment (UE). The major difference between CNPC and UAV payload communication is that it requires a much higher data rate to initiate the transfer of full high-definition (FHD) video from the UAV to the ground user later [5]. However, it is anticipated that the commercially deployed 5G network would provide more diverse services that include massive machine-type communications (mMTC), enhanced mobile broadband (eMBB), and ultra-reliable low-latency communications (URLLC) [6; 7]. The crucial challenge for the cellular network of the upcoming generation would be ensuring the privacy of the communications messages. The presence of unwanted users, or more specifically known as eavesdropper, always makes the exchange of information between the transmitting and receiving end vulnerable to malicious attacks due to the openness of wireless communication systems. To safeguard data transmission over the communication network, physical layer security (PLS) has emerged as an effective solution to such confidentiality issues in wireless connections [8]. Sustaining proper encryption at the physical layer can efficiently increase the security level to high, and eventually, it will make the whole system more reliable and secure. Compared to other practical techniques, chaos-based encryption has become a prominent process to maintain high-level of efficacy as far as the security is concerned. In such technique, stealing of information becomes tremendously difficult for intruding users as the transmitter and receiver share an initial value exclusively between them. The [PERSON] mapping system is such a chaotic-based encryption scheme that enables a completely unpredictable numerical sequence of system variables. Furthermore, the addition of partial control variables to the design process in [PERSON]'s hyperchaos mapping system enhances the keyspace of the encryption algorithm [9; 10]. To provide high-quality eMBB services considering the robustness of the terrestrial network capacity and alleviate the effect of network congestion or network failure, a multi-UAV-aided non-orthogonal multiple access (NOMA) network is preferred in [11]. Such multicarrier NOMA technology-based UAV-terrestrial integrated network is considered for supporting fast communication service recovery or even enhancing the network performance.