4.2.6. Satellite Technology

Satellite technology is a solution for MG communication in remote places where cellular or other wireless technologies are not accessible. Furthermore, they can be applied as a redundant path for creating backup communication. There are three different satellite technologies, including Low Earth Orbits (LEO), Medium Earth Orbit (MEO), and Geostationary Earth Orbits (GEO). Table 5 shows the characteristics of satellite technologies. The major disadvantages of satellite technologies are high expense and high latency. However, LEO and MEO areas are being developed to improve latency and bandwidth. More service providers represent GEO, including Inmarsat, BGAN, Swift, and MPDS while just NEW ICO offers MEO. Iridium and Globalstar are operators of LEO [55,56].

#### **5. Wireless Technologies Roadmap and Future Trends for MG**

MG is one of the key elements of the developed power grid system, which is being widely used because of the aforementioned merits. Regarding wireless specification correspondence of MG remote and independent specification, in the previous section, features of wireless technologies and applications in each part of the hierarchical supervisory of MG are discussed. Table 6 depicts how the literature considers applying wireless in MG. As can be seen, the literature proves wireless communication benefits in MG according to different goals and examination methods. We classified them into control, standard, and technology-based categories. This table reveals a new approach to the role of MG in the power system, as an active element is under trial and error test by using new enhancements of wireless technologies [52,57]. Concerning countless merits of wireless technologies application in MG, it is necessary to determine a roadmap clarifying the future path of this enhancement. To provide a roadmap for applying wireless technologies in MGMS, we should consider the following aspects.

#### *5.1. MGMS Structure Development*

New wireless technologies should consider communication specification requirements of MG application such as bandwidth, latency, and security. To provide a mechanism for applying wireless in MG, we require a definition of unified information exchange and standard. The unified model should be flexible to apply in the different control structures of MG depending on the extent, application, and geographical location of MG. As discussed before, MG can be centralized or decentralized. One of the promising strategies in distributed control of MG is MAS, which facilitates control of MG and assists the SG concept approach in reality by accommodating self-healing characteristics for the power grid [7,58–61]. In the MAS environment, every element of MG can interact and cooperate with other elements intelligently to achieve power system global objectives, as can be seen in Figure 4. In this case, although there is no "one size fits all" approach, robust technologies such as 5G can be deployed in two control architectures. Central control of MG can derive active power and reactive power of load information and control generation portion of each power resource in MG by applying 5G communication and cloud computing at the edge. It is also possible for 5G employment in decentralized MG control based on droop control power, which needs real-time reference control signals, large distance coverage, and security [62]. As well as the independent grid characteristic of MG, there are new aspects in the smartization of MG, making it an integrated part of the public grid, which is the main hypothesis of this paper. MG as an AS of the main grid is one of the aspects, which will be an incentive for penetration extension of MG as it provides profit for owners. Such aspects require the contribution of technologies in MG such as V2G, smart inverter, etc. Wireless technology is a good candidate as a communication infrastructure of these technologies [63]. AS provision of the main grid, including frequency regulation, voltage control, and black-start aid by MG needs its communication characteristics, especially time constraints, which can be met by 5G mm-Wave characteristics offering fast, reliable, and robust interacting [64–67].
