# Analysis of AMI Communication Methods in Various Field Environments
## 6 Discussions
### Discussions on the Power Line Communication
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Residental** & **Commercial** & **Rural** & **Factory** & **Underground** \\ \hline \(\alpha\) (dBm/m) & \(-0.212\) & \(-0.135\) & \(-0.074\) & \(-0.145\) & \(-0.127\) \\ \(\beta\) (dBm) & \(-28.8\) & \(-31.6\) & \(-31.2\) & \(-28.3\) & \(-38.1\) \\ Average noise power (dBm) & \(-47.2\) & \(-43.2\) & \(-40.0\) & \(-43.4\) & \(-49.6\) \\ Maximum noise power (dBm) & \(-39.5\) & \(-33.0\) & \(-34.0\) & \(-35.1\) & \(-38.6\) \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of the regression model coefficients for PLC signal and noise powers at various areas. The SNR model at the Overhead Rural Area is shown in Figure 30c. At this area, the SNR curve has the mildest slope among the five types of areas. This is because the power lines at the Overhead Rural Area have only a few branches. However, the average noise power is larger than those of any other types of areas. This is due to the solar power systems that the houses in rural areas have. The solar power system usually generates a lot of background noise. The 0 dB SNR value of the average and minimum SNR values occur at 120 m and 38 m, respectively. These points are marked as vertical red and blue dotted lines, respectively. The measurement results for PER at the three sites are also given in Figure 30c. The SNR model at the Overhead Factory Area is shown in Figure 30d. The slope of this area is less steep than that of the Overhead Residential Area. The PER results are also shown in the figure. At the Overhead Factory Area, PER measurements are taken at 6 MPs. For Site 4-3, there are two MPs at the distance of 10 m and both MPs have the same 0% PER value. At the distance of 10 m, Site 4-1 also has an MP. However, the PER value at this MP is 100%. Even though they have very similar distances from the transmitters, the PER results could be quite different depending on the local noise. For the case of the Overhead Factory Area, we usually have strong inductive loads, such as powerful electrical motors. Note that these loads can cause strong background noise over several MPs and make the communication quality unpredictable. The SNR model in the Underground Area is shown in Figure 30e. In this area, the slope of the SNR is less steep than that of the Overhead Residential Area. The received power is rather small compared to those of other areas. Moreover, the maximum noise power is quite large, resulting in a very low minimum SNR even at MPs that is close to the transmitter. The difference between the maximum and average noise powers at Underground Area is 11 dB, which is larger than the cases of the other areas and thus yields a wide Gray Zone. When preparing for the measurements in the Underground Area, it was not easy to find a point where the underground line is fully deployed from the transformer to its customers. The MP of Site 5-1 has a mixed type of Figure 1c with a 15-m overhead line and 5-m underground line as mentioned in Table 1. The overhead line is known to provide better channels for communications than the underground line case. Since the underground line is not long, the channel environment of the MP at Site 5-1 is not bad. As a result, this MP shows 0% PER. Site 5-3 is an apartment building, where the power line is inside the building not under the ground. The first MP of Site 5-3 is placed on the first floor of an apartment building and shows 0% PER. Site 5-2 has a ground transformer, which is connected to houses, stores, and a kindergarten through long underground lines. Due to the long underground path, the SNR of the received signal is very low and the PER is shown to be 100%. From these results, we can find that the communication performance of HS PLC is poor in an underground environment. We can expect that PLC modems, which are recently developed with new technologies, such as HPGP [36] and IoT PLC [37], can provide better communication performances, especially for the underground environment.