## 2 System Model  
The proposed system model and the dynamic time allocation scheme based on spectrum sensing are shown in Figure 1 and Figure 2, respectively. The system model consists of a BS, IR, HT, WiFi access point, ED\({}_{n}\) (\(n\) = 1, 2,..., \(N\)), and jammer. The BS is a signal emitter that broadcasts in the environment and transmits its information to the IR. HT uses the communication infrastructure of the BS and delivers its own information to the same receiver in a symbiotic relationship with it. ED\({}_{n}\) overhears the information BS and HT sent to IR. The jammer is a friendly terminal that prevents information leaking to ED\({}_{n}\). The WiFi access point placed in the same cell, i.e., indoor as the HT is a terminal that partially supports the energy harvested by the HT with the signal it emits. A full period in the dynamic time allocation scheme is normalized as \(T\) = 1 s, whether the BS is active or passive is detected by HT at time \(\beta_{0}\). When BS is detected to be active, \(\beta_{1}\) time is the bit transmission time of BS to the IR. HT works as a relay during \(\beta_{1}\), and helps the signal transmission of the BS with the backscatter communication technique. Additionally, HT harvests energy from the signal of BS, jammer and WiFi access point. When the BS reaches the minimum number of bits that must deliver to the IR to meet Quality of Service (QoS), it cuts off the signal it sends to the IR. In this case, the HT has the opportunity to transmit its own information to the IR. During \(\gamma\beta_{2}\), HT-IR connection is established with active data transmission (or traditional communication). Here, \(\gamma\in[0,1]\). In the \(\gamma\beta_{2}\) period, the BS works like a jammer to disrupt the information leaked by the HT to the ED\({}_{n}\) and reduces the SNR value in the ED\({}_{n}\). When BS is detected to be passive, unlike the previous situation, HT harvests energy during \(\beta_{1}\), and does not carry out backscatter communication. It transmits signals to the IR with active data transmission, using energy harvested for the \(\gamma\beta_{2}\) period. This scenario is known only as energy-harvesting-then-transmitting protocol in the literature, and is widely preferred in wireless powered communication networks [11; 53; 54]. In the system model, the WiFi access point continues to emit a signal throughout the entire period, while the operating time of the jammer is \(1-\beta_{0}\). It is assumed that the perfect SIC technique is used at IR to recover the signals transmitted during \(\beta_{1}\)[55]. Four different operating modes for HT are shown in Figure 3. The spectrum sensing unit detects the activity of the BS with energy detection-based spectrum sensing. During this process, the energy required for HT is met from the initial energy \(E_{i}\). The energy harvesting unit allows the HT to harvest energy from the BS, jammer, and WiFi access point that emit signals to the environment. The battery is charged with the harvested energy. The backscatter circuit is one of the most important reasons why HT has a hybrid structure. While in similar approaches, the user has a structure that can transmit signals with traditional communication, here, the backscatter feature is included and a low-power communication model is designed. In the backscatter circuit, a part of the signal coming from BS to HT is absorbed, while a part of it is backscattered to the IR through passive communication using antenna impedance mismatch. The symbiotic relationship between HT and BS is due to the ability of HT to communicate by backscatter. The harvested energy is used from the active transmission unit. Thus, HT sends its own information to IR with high signal power. This unit represents signal transmission through traditional communication.