## 2 Related Work
The DC component issue is resolved due to the usage of the negative voltage level, but the synchronization problem still exists in the polar method. NRZ uses two signal levels, positive and negative. NRZ-L is based on two voltage levels for signal representation. It helps the receiver to distinguish between positive and negative bitstreams. Synchronization still has issues in the case of 0 s and 1 s. RZ provides a good solution to transmit the 0 and 1 bitstreams over the network. The 0 s bitstream is not ignored like a previous digitizing scheme. RZ consumes double bandwidth to transmit bits over the network. Biphase is a third digitizing scheme of the polar method. Biphase is further divided into two categories, which are Manchester and Differential Manchester [13]. Manchester digitizing helps the receiver to understand the bit pattern. The authors presented power spectral density (PSD) for the nonlinear self-interference signal in a theoretical way, and the estimation method of PSD was developed for nonlinear self-interference [14]. Furthermore, the convergence performance of the canceller was improved by the proposed selection technique. The results show that the proposed method can achieve similar cancellation performance compared with the original frequency-domain Hammerstein canceller and a time-domain nonlinear canceller. The proposed approach improves the computational cost, but it requires a high-speed communication link. Furthermore, the DC component problem is not there. Double bandwidth is required in case the signals are toggled from 0 s to 1 s or vice versa [15; 16]. Signal variation is decided in the middle of a transmission. The Differential Manchester digitizing scheme deals with synchronization issues in a better way. However, it requires a double bandwidth to transmit toggle bits. On the other hand, the high performance of the receiver is required in case of the same long streams. The rapid variation does not determine which bit is being transmitted over the network [17; 18]. The bipolar method is another coding scheme which is further divided into three main subcategories: Alternate Mark Inversion (AMI), Binary 8 Zero Suppress (B8 ZS), and High-Density Bipolar Order 3 (HDB3). Bipolar provides a satisfactory solution to the problems of synchronization, DC, and double bandwidth concerning other digitizing schemes. The AMI technique offers a better solution than all previously discussed digitizing schemes. In a long stream of 1 s, the receiver can quickly determine each bit. It provides a negative to positive jump in the case of 1 s bit signal modulation [19]. There is no DC component issue; no double bandwidth is required to transmit signals. Zero voltages are used to represent bit 0 s. On the other hand, it does not guarantee that the receiver will correctly receive the signal [20]. There are many issues interlinked with digital and analog signal modulation, like bandwidth utilization, the power spectrum, the short and long range of the signal, signal connectivity, etc. Therefore, several modulation techniques have been designed to resolve these issues in the domain of digital modulation, analog modulation, and multi-level modulation for network communication. Table 1 shows the related work summary against the benchmark techniques, whereas, Figure 2 presents the hierarchy of the possible existing modulation techniques for network communication.