## 5 Deployment of PLC for Smart Metering and Smart Grid Systems
### NB PLC Systems for \(LV\) Grid Communications
#### 5.3.2 High Level System Aspects  
One fundamental characteristic of PLC systems in LV grid for Smart Metering purposes is that node locations are basically fixed. Typically, PLC signal injection takes place at SSs, in the secondary winding of MV to LV transformers. In Smart Metering systems, service must be delivered at the locations where smart meters are installed. There is no feasible way to modify the location of neither the SSs, nor the meters, as the latter are associated to the points were electricity service is delivered, and that location is the choice of the customer. This situation can be considered not too different from other technologies, where end service points are fixed. However, the main difference is based, first on the number of end-points, and second on the great difficulty to gain access to intermediate grid positions, where network nodes might be also installed to configure the desired network to fulfill given quality objectives. LV grids are indeed not an homogeneous set, but it is very common to find underground LV cables with low to inexistent access to them. Of course, there are also LV grids which make extensive use of both LV cables laid on walls or suspended on poles, where cable access could be easier. Both cable deployment structures can be found mixed in the different utility service areas, with a trend to find underground scenarios in urban areas, and overhead in suburban and rural areas. In any case, as this circumstance cannot be controlled by the electricity distribution company when facing a Smart Metering deployment, the situation implies that traditional telecommunications planning is virtually impossible, and system communications must rely on the existing nodes on the grid, that are in fact the service destination nodes.  
The situation explained above has already been addressed from a network node functionality perspective in most modern NB PLC systems [94,95,142,143] with a variable degree of success. The way this issue has been addressed is through the definition of a \"node repetition\" functionality that utilizes the capillarity and big number of network nodes, to create a packet transport structure that allows any packet to reach any destination through the help of the nodes in the grid, e.g., PRIME system names this repetition functionality as \"switching\", and bases this layer 2 capability in the ability of every node in the network to act as a \"switch\" to repeat (retransmit) any layer 2 packet which is intended for a node that hierarchically depends on it. The creation of \"switches\" is managed by the controller of the subnetwork, _i.e._, the Base Node, that decides which service nodes are allowed to act as \"switches\" to help him cover the entire grid. The success of the layer 2 (e.g., PRIME) or layer 3 (e.g., G3, with 6 LoWPAN [144]) protocols capable of defining the repetition solution is based in a combination of physical layer available throughput, together with the smart definition of the algorithms and packets structures to make repetition functionality subject to an agile implementation, capable of fulfilling close to the real-time objectives of technologies needed for Smart Metering systems as part of the bigger Smart Grid concept.