## 2 M-QAM SD-PLC System Model  
The M-QAM SD-PLC system is a digital communication platform that is highly adaptable, programmable, and intelligent. It performs complex operations simultaneously so that data processing and transfer over the electrical power network can be done efficiently, reliably, and synchronously. With the help of this platform, binary data produced by the PLC transmission system may be generated and sent utilizing a wide range of intelligent digital communication techniques, digital signal processing (DSP) algorithms, SDR, and digital and analog operations across the network. The use of programmable hardware is more economically advantageous when choosing a design platform for a reliable communication system. The same hardware architecture can be used to build multiple communication system scenarios, and the software architecture is easily changed. Second, a digital environment allows for much more precise control of the software and hardware parameters, such as the generated signal bandwidth, oscillator phase and frequency, and filter response. Lastly, intelligent software and hardware for digital signal processing make it easy to use algorithms for data generation and transmission, synchronization, data compression, encryption, data reception, and error correction. Moreover, these algorithms are essential for modern digital communication systems' development. As a result, the aforementioned factors influenced the decision to conduct this research using a flexible SDR design approach. This section describes the process of developing digital transceiver systems with SD-PLC. To achieve the primary goal of this study, these systems employed M-QAM modulation schemes and SD hardware for real-time data transmission and reception over an in-house power line channel. Furthermore, the SD hardware is highly flexible, re-programmable, re-configurable, and can be customized using the universal software-defined radio peripheral (USRP). Figure 1 illustrates the architectural layout of the M-QAM-based SD-PLC transmitter and receiver system utilized in this research. National Instruments (NI) subsidiary Ettus Research developed and manufactured the SD hardware platform used in this study. A flexible SD transceiver, the universal software-defined radio peripheral (USRP), is used in various communications applications. It is a robust, modular, and utterly programmable SD device. As depicted in Figure 1, the coupling of the USRP transceiver, the PLC coupling circuits, the power outlet serving as the channel, signal processing software, and personal computers (PCs) facilitates the prototyping of PLC systems. The USRP N210 with LFTX transmitter and LFRX receiver daughterboards was connected to an Ethernet network, and the transmit and receive power line coupling interface was used to connect to the PLC channel to facilitate the real-time transmission and reception of data with the MATLAB and Simulink software. Connecting the transmitter and receiver to the PLC channel required coupling interfaces, which are also crucial components of the PLC system. It acts as a filter, blocking the power signal while letting the communication signal pass through the channel. It also provides galvanic isolation to protect the sensitive parts of the transceiver from the mains voltage [6]. Connecting PLC transceivers directly to the electrical network poses challenges due to the intricate nature of the loads connected to power networks and the variability in the impedance at the connection point. The proper coupling interfaces for the sending  
Figure 1: The M-QAM SD-PLC transceiver’s architecture. Adapted from [31]. and receiving of data must be constructed or selected to send and receive data over an LV indoor SD-PLC channel. This study used the USRP transceiver and an off-the-shelf coupling circuit from STMicroelectronics called the STEVAL-XPLM01 CPL to send and receive data over the SD-PLC channel. Figure 2 depicts the M-QAM SD-PLC transceiver system.