# Grid Nodes Selection Strategies for Power Quality Monitoring
## 4 Problems and Future Prospects
### PQ--Part of Smart Grid and Its Communication Network
Criteria will be related to optic fiber availability in a substation, reference signal received power (for cellular communication), or other aspects of signal propagation, EMC limits, and hygiene norms; in addition, the required investments for infrastructure, bandwidth licenses, and bills for communication services. However, from our point of view, the best example of remote PQ monitoring is given in [24], in which many communication problems were encountered with less than 50 monitors. According to IEEE Std 2030, each investigation (in the field of ICT) should be started from the analysis of data flow characteristics, and a classification table is proposed forthis purpose. The table with an insignificant expansion for PQ application is presented in Table 7, since the table and the approach has not been met in the PQ literature. A \"Data aggregation\" row is added to the table since it is important for PQ: despite PQ events being expected at every moment, they should be aggregated into larger time intervals, which is directly related with data packet structure. A tight requirement for the delay is not needed, but the accuracy of time synchronization (monitors synchronicity) is very important for avoiding excessive PQ events counting as voltage sags in [20]. PQ data are transmitted from the end-node to the hub; thus, the application works in unicast mode. Currently, PQ data are only informative, but later, after amendments in legislation, they will become more critical. Despite low requirements for data provision reliability, PQ analyzers' resistance is necessary to both intentional EM interference (IEMI) and high-altitude EM pulses (HEMP). Currently, security issues, such as unauthorized access, are not critical. Later, security issues will gain an importance for legal disputes. Moreover, if the PQ system is integrated, for example, with relay protection and automation, the strictest requirements for data security must be introduced (to ensure correct grid operation, prevent cyberattacks). A Smart Grid communication network is classified into three main coverage areas: wide area network (WAN), neighborhood area network (NAN), and home area network (HAN). In addition, many specific groups can be derived: low power wide-area network (LPWAN), industrial area network (IAN), local area network (LAN), etc. [27; 29]. It is obvious that PQ monitoring is s WAN application where the data rate from the end-node should be reduced with feature extraction in the stage of local analysis (see Figure 1). Feature extraction is an important factor to lower requirements for ICT and avoid channel jamming. Table 8 summarizes bandwidth and coverage of main ICTs which are suitable for Smart Grid applications, and contributes to the clarification that data rates must be diminished as much as possible in the case of a massive monitoring system. Main WAN alternatives  
Figure 9: Extension of traditional power grid planning and development concept: PQ layer incorporation is essential to sustainable development. with high data rates are as follows: WiMAX--1 Gbps (802.16 m), cellular network (e.g., HSPA+--168 Mbps in downlink and 22 Mbps in uplink, LTE-Advanced--1 Gbps in downlink and 500 Mbps in uplink), and fiber optics--1-40 Gbps typical. According to [27], some fiber optic pilot projects have been executed with terabytes or petabytes bandwidths; however, high cost is a key factor limiting the usage of power optics. In the case of [24], 4G LTE has been selected for WAN; however, cellular service can be expensive. LPWAN technologies--LoRa or NB-IoT--can be applied when it is possible to reduce bandwidth to 20-50 kbps. Obviously, the whole list (given in Table 8) is applicable to designs of PQ communication network: WAN ICTs are suitable to be utilized in a backhaul network, the alternatives--for lower-in-hierarchy levels such as backbone and LAN.