## 4 Status of PLC in Smart Metering Systems  
PLC is mentioned at the natural media to connect meters in Smart Metering systems [22]. Many of the PLC technologies that have been developed through recent history are discussed in [51,82]. Reference [9] provides a consistent organization and classification of these systems, with an especial focus on their standardization status. However, most of the references on PLC for AMR just analyze the nature and structure of the systems [19, 20, 21], with no clear reference on implementation or specific communication performance results. BB PLC has been extensively developed for in-home and Internet access, as the existing standards show [47,48]. There are references [83,84] to the use of BB PLC for Smart Grid applications, but not many go further that the technology assessment and adaptation proposals for specific Smart Grid services (OPERA 2--second phase of OPERA project- published a deliverable assessing the feasibility of a BB and NB combination for Smart Metering [85]). Reference [86] refers to the usage of BB PLC for Smart Grid backbone connectivity, and Reference [87] includes recent examples of such deployments among a group of many other PLC applications. In [88, 89, 90], the utilization of BB PLC systems for Smart Grid applications is explored, but no major deployment of BB PLC as far as the smart meter, exists (there are, however, references to small scale pilots, such as the one in [91]). Reference [92] gathers most of the relevant information to develop MAC layers for PLC systems, depending on the intended application. Reference [93] refers mainly to NB PLC systems when elaborating on the options for the MAC. Smart Metering is the most recent Smart Grid application based on PLC that uses NB PLC systems especially in Europe. The PRIME system is one of the systems used [94]. G3 [95] is another system of a similar nature [96,97]. PRIME system is being deployed extensively by Iberdrola in Spain [98]. PRIME technology evolution, from inception to field performance tests, can be followed in [68] where initial ideas are presented, and [36,99,100] covering the evolution of PRIME technology, from the early dates of PRIME's first implementation with interoperability assurance, to the first demonstration deployments, and the full deployment (over 100,000 smart meters) of a complete Smart Metering solution. Regarding the G3 system, references to small-scale field tests can be found [101, 102, 103, 104], but no massive deployment result is known to date. G3 and PRIME are the basis of the most recent standardization efforts in IEEE (1901.2 [105]) and ITU (ITU-T G.9903 [106] and 9904 [107], respectively). Many of the tests and experiments cited and used in this paper are PRIME PLC technology based, and are representative of the behavior of new state-of-the-art HDR NB PLC systems. Regarding PLC devices, references [108, 109, 110, 111] analyze modems and their coupling interfaces. There are also some references [112, 113, 114] focused in the injection of PLC signals (mainly in the MV grid, as LV grid is less difficult), in the primary winding of the distribution transformers. A small quantity of papers focus on the characteristics of the communications devices for PLC communications in SSs as a harsh environment [115], and some other references discuss three phase nature of LV in substations [116, 117, 118]. Some recent studies deal with single phase-single transformer PLC injection [119,120]. LV grids are the next step of the segments to be controlled in utilities' grids. This control cannot take place without real-time telecommunication systems to access the grid. If PLC systems are to be deployed over the LV grids for Smart Metering purposes, real-time PLC systems should be offeringthe telecommunications for control systems on LV. Real-time PLC systems are many times associated to BB PLC systems.