## 2 State of the Art  
A standard power grid transmits energy from the power supply to end customers via high-voltage (HV) overhead lines, then MV lines and LV lines close to the final destination of energy consumption. In Smart Grids, CPEs (slaves) installed on a customer's property send data upwards in the communication hierarchy within the distribution segment of the power grid. Usually at LV/MV substations, data are concentrated and sent towards the network operational center [26]. For such transmissions, an optical network or other means of data transmission can be used. If no such technology is present, transmission can be provided by PLC technology [27]. Especially in such cases, BPL can serve as a bridge technology towards the closest optical network interconnection point [28]. From LV/MV substations, data can be sent towards the transmission part of the power grid network-MV/HV substation, where flow significantly increases towards the backhaul interconnection network point. Network topology and communication needs of different devices on the network reveal demands on reliability, latency and data rate [29]. An example of a communication scenario with usage of power line communication on LV and MV is shown in Figure 1. Resulting from lower traffic volumes, with no extra need of low-latency response, usually NB-PLC can be used for data transmission from buildings towards LV/MV substations. Summed traffic transmitted over the MV network reaches higher volumes, and thus usage of BB-PLC is recommended [30]. If devices with the ability to indicate fault detection are also present on location, the network has to provide low-latency service to fulfill the needs of communication protocols which are used for such purposes (e.g., IEC 61850) [31]. In terms of BPL implementation on the MV, attention has to be paid to the choice of proper coupling method [32]. For underground power distribution, usually inductive couplers are used since they more easily maintain good levels of electrical insulation [33]. To improve parameters, usually an air gap in the coupler is increased [34], which might lead to significant increase in both weight and volume of such a coupler. Signals that are transmitted through power lines tend to being attenuated by the transmission environment properties of power lines, which also increases over distance and frequency [35; 36]. Attenuation is also partially determined by devices placed along the power grid (e.g., transformers), which highly influence impedance at a particular frequency range among cable lengths and spacings between them [29; 37]. More importantly, knowing such characteristics is beneficial in terms of designing good PLC solutions [38]. Since the frequency determines a signal's behavior and attenuation, frequency bands are also chosen depending on the country where the system is being deployed, and its purpose and therefore volume of traffic are expected in both directions. Wider bands enable higher data throughput, but higher frequencies are more attenuated over distances. When the signal attenuation is too high, then the transmitted data might not arrive at the receiver side. To overcome this problem, the usage of a repeater is required [39]. Unfortunately, deployment of repeaters introduces certain degradation of network throughput as a result of its operation [40]. Repeaters re-amplify and re-package the signal to restore its previous signal level; thus, compensation of attenuation along a power line is achieved. To transmit signals over long distances, repeaters are used to overcome losses resulting from physical characteristics of the powerline. Depending on the distances involved, electric utilities often have to install repeaters to maintain signal strengths within acceptable limits. Increasing the number of involved nodes always leads to a decrease in throughput and increase in latency [41]. Another important factor influencing data transmission within PLC network is noise [41; 42].