# Wireless Communication Technologies for Smart Grid Distribution Networks +
## 4 Previous Studies on Selecting Suitable Technologies for Power Line Monitoring
In a second experiment, the communication performance was evaluated at a distance of up to 700 m between two nodes in outdoor conditions. The results of both experiments are shown in Tables 3 and 4. The test results showed that the high current did not affect the communication performance. However, the obstacles between the two communication nodes significantly affected the performance. Even though the communication performance was degraded, outdoor transmission at a distance of up to 400 m was achieved with a transmission success rate of up to 80%. The effect of high voltage, mainly due to the corona effect, will be validated in the future. State-of-the-art sensor communication technology for sensing nodes on power lines, as discussed in [19; 20], was implemented usingZigBee technology based on IEEE 802.15.4 in the TI's CC2530 SOC solution. It should be mentioned that this technology is comparable to Bluetooth but with the added advantage of very low latency. The sensor uses an 8051 MCU, 256 KB flash, 8 KB RAM, 12-bit ADC, and eight channels. It takes 400 ms to communicate and go back to sleep. At 100 A, the operational frequency is as high as once every minute. Energy storage ensures 13 cycles of operation after an outage. As previously mentioned, review studies on smart grid communication technologies, such as [3], have recognized that a big challenge in this area is the difficult estimation of the instantaneous value of the wireless link quality. From all the real-world studies on WSNs where different sensor platforms have been used, the common observations are:  
* The recognition of three distinct reception regions in a wireless link: connected, transitional, and disconnected. * Wireless link quality varies over space and time, unlike standard models often used in simulation tools. The coverage area of sensor radios is neither circular nor convex, and packet losses are common at a wide range of distances, varying over time. * Link asymmetry (one-way communication) occurs when the transmit power is low. A measurement of the link quality was performed by [PERSON] et al. [14], using sensors implementing IEEE 802.15.4. They used a packet length of 30 B and a buffer size of 64 packets. The experiments were conducted in three locations: an outdoor environment near a 500 kV substation, inside a power control room, and in an underground transformer vault. The channel was modeled as a log-normal shadowing path loss, where the Signal-to-Noise Ratio (SNR) \(\gamma\) in dB, was expressed as  
\[\gamma(d)_{dB}=P_{t}-PL(d_{0})-10\eta\left(\frac{d}{d_{0}}\right)-X_{\sigma}-P _{\eta} \tag{1}\]  
where \(P_{t}\) is the transmit power in dBm, \(PL(d_{0})\) is the path loss at the reference distance (\(d_{0}\)), \(\eta\) is the path-loss exponent, \(X_{\sigma}\) is a zero-mean Gaussian random variable with a standard deviation of \(\sigma\), and \(P_{\eta}\) is the noise power in dBm. For different propagation environments, the values of \(\eta\) and \(\sigma\) were calculated from the measured data using linear regression. The results for these parameters are presented in Table 5. Two links for communications were also considered: line of sight (LOS), and non-LOS (NLOS). Noise and interference were measured using a TinyOS application that samples RF energy at 62.5 Hz by reading the Received Signal-Strength Indicator (RSSI) on a CC2420 radio in the various aforementioned environments. The noise meas \begin{table}
\begin{tabular}{c c c} \hline \hline
**Propagation Environment** & **Path Loss (\(\eta\))** & **Shadowing Deviation (\(\sigma\))** \\ \hline
500 kV substation (LOS) & 2.42 & 3.12 \\ \hline
500 kV substation (NLOS) & 3.51 & 2.96 \\ \hline Underground transformer vault (LOS) & 1.45 & 2.45 \\ \hline Underground transformer vault (NLOS) & 3.15 & 3.19 \\ \hline Main power room (LOS) & 1.64 & 3.29 \\ \hline Main power room (NLOS) & 2.38 & 2.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mean power loss and shadowing deviation in different electric power environments, as measured by [PERSON] et al. [14].