## 5 Deployment of PLC for Smart Metering and Smart Grid Systems
### NB PLC Systems for \(LV\) Grid Communications
#### 5.3.1 Low Level System Aspects  
Low level system aspects are related to the basic physical layer of the PLC technology. Modulation is one of these important aspects, to be determined based on the existing physical conditions and limitations of the grid (mainly distance and noise). Modern multicarrier modulation systems based on OFDM generally offer different modulation alternatives, trying to get the most of the state-of-the-art electronics, and at the same time offering maximum throughputs in benign communication channels. However, grid conditions do not always favor the usage of high throughput (and low noise immunity) modulations. Although PLC systems typically behave in an adaptive way to select the most convenient modulation for any given channel conditions, the feature does not come without the cost of burdening channels with control packet overhead to manage link conditions that might reduce the useful throughput. Smart Metering systems rarely tend to establish high duration communications with a meter, but rather tend to adhere to the polling procedure of getting meter reading one meter at a time. This fact, together with the circumstance that in open and interoperable systems, peers needing to adapt the modulation scheme might be taking non-optimal decisions based on the assumption that its peer has some sensitivity characteristics that are not real (e.g., PHY Robustness Management (PRM) is a feature that in PRIME systems allows to adjust modulation scheme--robustness and power--of the individual links in an end-to-end connectivity; this feature would need to precisely know the sensitivity of the peers to perform properly, as the assumptions and, subsequently, PRM messages may lead to build unstable subnetwork topologies), the possibility of establishing a fixed a modulation scheme is attractive to decrease system complexity. As a complement to the above, the data provided in [36] is very useful to understand that the PLC communications layer is just one of the parts of the system. According to [36], Smart Metering systems make common use of DLMS/COSEM-like application layers [137], and work in such a way that a central element (the concentrator, placed usually at the SS) performs a polling procedure to get all the meter readings. The overhead described is such that the performance decrease produced from physical layer throughput to application layer meter readings can be calculated with a factor in excess of 200. Thus, and taking PRIME modulation maximum throughputs with different modulation schemes as a reference [138], a factor of 6 (the ratio between the maximum and the minimum throughput with PRIME) is not relevant in the overall throughput performance. On the other side, PLC communication channels in LV electricity grid are harsh and exhibit an instantly changing nature (see summary of noise contributions in [139]) that may produce unavailability in channels working with Signal-to-Noise ratio (SNR) close to the limit of the electronics behind. The circumstance is exactly that of radiocommunications [140], where links are designed to allow for an instant fading of a certain quantity, as there is statistical evidence that such a circumstance will appear. There are studies on the nature of PLC channels modeled in terms of noise [141], but there is not a quantification of the fades or the statistics behind as probably the effort needs to study a representative amount of LV grid segments at the utility side of the grid, in different regions of the world. In the absence of such studies, a conservative choice of the lowest risk modulation is appropriate for a field deployment. This modulation scheme should be accompanied by an errorcorrection scheme, e.g., in PRIME PLC systems this would be DBPSK with Forward Error Correction (FEC) that offers 20 kbps throughput at physical layer. According to the PRIME cases studied in [100], the usage of DBPSK modulation with FEC produced application layer availability over 90%. There are other low level aspects that deserve attention.