# State of the Art and Trends Review of _Smart Metering_ in Electricity Grids
## 3 Smart Metering Technologies
However, as the electricity grid was not conceived for data transmission, it is a harsh medium and communications are subject to disturbances due to spurious emissions and supra-harmonics from the devices connected to the grid (inverters, turbines, lamps, and appliance engines, among others) [36]. The _PLC_ frequency bands differ from one region to another. In Europe, _PLC_ is regulated by CENELEC and specifies four different bands: energy providers (standard and proprietary protocol), users (standard and proprietary protocol), users (_CSMA_ access), and users (standard protocol) from 3 to 148.5 kHz. FCC regulates the ranges in the United States (10-490 kHz), ARIB in Japan (10-450 kHz), and EPRI in China (two bands from 3 to 500 kHz). Two main groups can be distinguished among _PLC_ technologies: (i) _Broadband PLC_ (_BB-PLC_), which uses frequencies up to 30 MHz and enables high data rates; and (ii) _Narrowband PLC_ (_NB-PLC_), which uses frequencies up to 500 kHz and provides moderate data rates. _NB-PLC_ is currently experiencing an expansion due to its good performance, a consequence of adapting advanced modulation techniques such as _OFDM_. Although its data rates are moderate, it is sufficient for _Smart Metering_ applications. _NB-PLC_ is especially popular in Europe, where nearly all countries have performed at least a pilot, and a wide range of deployments use this technology. Among _NB-PLC_ standards it is worth mentioning _G3_, _PRIME_, and _IEEE 1901.2_. Poland and Spain have performed massive deployments using _PRIME_ while Japan, France, and Luxembourg have used _G3_. Both _IEEE 1901.2_ and _G3_ offer \"phase detection,\" a popular feature that allows the node coordinator of the network to determine on which phase a single-phase _SM_ is connected. Then, the utility can balance the power demand across the three phases and improve the quality of the supply [41]. _Digital Subscriber Line_ (_DSL_) is also a popular wired technology that uses the wires of the voice telephone network. Its main advantage is that in most cases the medium is already deployed and the data rates are quite high. Hence, some companies have chosen _DSL_ technology for their _Smart Metering_ projects, such as Stadtwerke Emden in Germany by Deutsche Telekom, where _DSL_ is used to transmit the consumption information from customers' premises to the municipal utilities [42]. However, the maintenance cost of _DSL_ is high and its efficiency decreases with distance. It is worth mentioning _Euridis_, a low-cost solution, well known (it was first introduced in the early 1990s) and with a long history of deployment (approximately 6 million _SM_s worldwide use this technology). _Euridis_ allows simultaneous access to up to 100 _SM_s connected in the same bus and it is considered the unique existing standardized interface for _Smart Metering_ applications over twisted pair cable. It is part of the IEC 62056-31 standard [43]. A considerable number of _SM_s in France are equipped with a _Euridis_ interface [44]. Finally, the fiber optic, well known for its very high data rates and noise immunity over several kilometers, has experienced a moderate expansion due the cost of deployment, especially if it is only used in the _SG_ context. For this reason, its use in _Smart Metering_ systems is limited to the Medium Voltage network and as a communication backbone in the transmission network by connecting _DCs_ and _CCs_. _Passive Optical Networks_ (_PON_s) are the most suitable option for _Smart Metering_, since they use optical splitters and one single fiber can serve several end-users. Within the standardization process, it is worth noting the work conducted by CENELEC, which has developed more than 60 standards and has 40 more underway. Additionally, CENELEC has joined forces with CEN and _ETSI_ (_European Telecommunications Standards Institute_), coming into the _Smart Meters Coordination Group_ (_SM-CG_).