# Analysis of AMI Communication Methods in Various Field Environments
## 6 Discussions
### Discussions on the Power Line Communication  
Using the signal and noise powers measured in Section 5.1, SNR values at each point can be calculated after the relationship of (6). These SNR values can be used to evaluate whether a point can achieve reliable communication or not. In Table 2, coefficients for the regression models and noise powers are summarized for each area. For the received power, there is a regression curve. However, for the noise power, there are two values; one is for the average and the other is for the maximum noise powers. Therefore, two SNR curves with respect to the distance can be calculated; one is for the average SNR and the other is for the minimum SNR. The average SNR is the mean value of the SNRs at a given distance and the minimum SNR is the lowest SNR at that distance. In PLC environments, various factors, such as the number of branches, path lengths, and types of loads, can affect the SNR values. Thus, different SNR values can be observed even though the MPs have quite similar distances from the transmitters. The calculated SNR curves are illustrated in Figure 30.  
Figure 30a shows the calculated SNR curves with respect to the distance at the Overhead Residential Area. The red and blue lines represent the average SNR and minimum curves, respectively. From this figure, we can estimate the average and minimum SNR values at the receiver of a given distance from the transmitter or the data concentrator unit (DCU). At all the 18 MPs of the Overhead Residential Area, the measured PER values are shown together in Figure 30a. Here, a PER value was obtained by 1000 MAC ping tests with a packet length of 128 bytes. In this PER measurement, only one-hop transmission is considered. The PER values at MPs are represented by symbol markers and the corresponding values are shown on the right vertical axis in percents. The PER values range from 0% to 100%. It is clear that higher SNR values at the receiver yield lower PER values. We can observe that the PER value shows a waterfall-like curve as the SNR value increases. In other words, if the SNR value exceeds a threshold value, then the PER value suddenly goes to 0%. For the average SNR curve, 0 dB of SNR is obtained at 87 m. This distance is indicated as a vertical red dotted line in Figure 30a. For the MPs, which are farther than this point, the PER values are seen to be 100%. We call this region the Poor Zone for convenience. With the minimum SNR curve, 0 dB of SNR is obtained at 51 m. This distance is indicated by a vertical blue dotted line in Figure 30a. In the distance range between the blue and red dotted lines, we can notice that some MPs have no packet losses (0% PER) and the others have complete packet losses (100% PER). If an MP in this range has a good channel environment for communication, then its PER is 0%. Otherwise, it will get packet errors even up to 100%. We call this region the Gray Zone. If an MP is closer to the transmitter than the blue dotted line, then the MP can have a lower PER value. In fact, most of the MPs in this region have PER values that are close to 0%. We call this region the Good Zone. However, MPs close to the blue boundary can have large PER values even though the MPs belong to the Good Zone. At Sites 1-1, 1-2, 1-4, and 1-5, all the MPs in the Good Zone have 0% PER. The two MPs close to origin at Site 1-3 have 0% PER. However, the PER of the last MP at Site 1-3, in which the distance is 35 m, is 99% PER. The SNR model obtained at the Overhead Commercial Area is shown in Figure 30b. At the Overhead Commercial Area, the slope of the SNR is less steep than that of the Overhead Residential Area. However, the average noise power is larger than that of the Overhead Residential Area. This is due to various noise sources, such as neon signs in stores. The average and minimum SNR values become 0 dB at the distances of 86 m and 11 m, respectively. These points are marked as vertical red and blue dotted lines, respectively. In Figure 30b, the measured results for PER are also illustrated.