## 3 Noise in PLC Networks
### Noise Library for NBPLC-PRIME
#### 3.2.3 Noise Signals Measured in Actual Operational Deployments  
In the process of capturing noise in the field, it is always tried to capture the noise peaks and the maximum noise accumulated during a certain period of time. This is because it is assumed that those maximums are the ones that are actually hampering communications. In general, these curves are included as maximum curves of the amplitude of the voltage versus frequency. However, it must be considered that the spectral distribution is not constant, but varies over time depending on the state of operation of the equipment generating the disturbances. Therefore, it is also interesting to have temporary records. In addition, it is necessary to know the electrical characteristics of the environment in which the noise is measured in order to reproduce that environment in the laboratory. The noise signal can be measured in power, as direct voltage or through the current, and in all the cases it is necessary to know the impedance on which it is measured in order to reproduce it precisely later on. Furthermore, in the context of AMI, noises do not affect all smart meters in the same way when they are operating at a high current or when they are operating at low or no current. The methodology and the instrumentation used also have a great influence on the measurements and therefore must be identified in the records that are delivered. For example, a record obtained with a power quality equipment for electrical networks registers harmonics with respect to the fundamental frequency with a limited frequency analysis and it is very different from one obtained with a specific RF system or with the own smart meters. Another relevant fact to keep in mind is that in the field it is always difficult to have 'clean' noises, understood as generated by a single disturbing source. The only elements that actually block a noise are the transformers. Therefore, below each transformer, the noises accumulate among each other. In AMI, each centralization is made up of multiple smart meters from which multiple noises can appear. The noise that comes from the load of a smart meter (i.e., household) is transmitted immediately to the rest of the smart meters nearby and can even affect more distant smart meters in a more attenuated way. With this accumulation of noise, it is difficult to determine the true source of noise. Only in relatively well-known environments or where a noise source operates exclusively at certain time periods, the source can be detected. It is understood, therefore, that some of the records available from the real environment will not be associated with a specific source, although the predominant source is indeed identified. Next, several noise records measured in operational power distribution networks of Union Fenosa Distribucion are presented with the aim of getting an idea of the main features that some of the noises identified in [54] present in actual deployments. In general, all the noises have been obtained as registers in the frequency domain, i.e., in a format that collects the voltage levels as a function of frequency at a given time. All recorded noise registers represent signals that are in the frequency ranges between 15 and 170 kHz, although the analysis focuses on PRIME frequency band (i.e., between 40 and 90 kHz). The equipment used for measuring the noise is a 4 PBN sniffer from ZIV [59], which allows the capture of instantaneous values and accumulated values of the frequency response of both noise and communications. The records are JPEG images with two lines: a colored one representing the 'instantaneous' noise, and a gray one, superior to the colored one, which reflects the maximum level measured since the analyzer was switched on, which is the sum of the noise and the PRIME communications signal. Nevertheless, the most important features of the measured noises are characterized in order to allow reproducing them in a controlled environment. Figure 8 shows the noise introduced by a community antenna.