# Analysis of AMI Communication Methods in Various Field Environments
## 3 Wireless Communications for AMI
### Measurements for the Wireless Communication  
In order to conduct wireless communications, we use a quarter-wave monopole antenna (Lirx Technologies Inc., Merlin, OR, USA, ANT-916-CW-HWR-SMA) with 5 cm \(\times\) 6 cm-ground plane for both master and slave modems, in which the antenna gain is 1.5 dBi. Here, the antenna unit is connected to the modem with SMA and N-type connectors through a 50 Ohm coaxial cable. Among the Wi-SUN channels, Channel 1, in which the center frequency is 920.7 MHz, and the transmitter power of 23 dBm are used to analyze the communication performance according to the following quantitative measurements:  
* Package error rate (PER): 1000 MAC ping test with the package length of 128 bytes
* Received power in dBm from Receiver Signal Strength Indication (RSSI)  
Both PER and received power through RSSI can be measured in Wi-SUN and ZigBee modems for practical field environments. We can also use a spectrum analyzer to precisely measure the received powers to examine a basic property of the wireless communications.  
For wireless communications, because the PER curve usually shows a rapidly increasing characteristic when it reaches communication distance limits, it is difficult to identify the status of communications before the distance limits. Hence, rather than the PER values, the received powers are further useful in quantitatively observing the communication characteristics of field environments.  
Here, the received power, which is denoted as \(p\), can be theoretically given as [35]  
\[p=-20\log(d)+27.6+2G_{A}+P_{TX}-20\log(f)\ (\text{dBm}), \tag{9}\]  
where \(d\) is the distance between modems and \(f\) is the carrier frequency in MHz. In (9), the constant \(G_{A}\) implies the antenna gain in dBi and \(P_{TX}\) is the transmitter power in dBm. To receive data at the receiver part, the received power \(p\) should be greater than the receiver sensitivity. For safe communication, the link budget between the received power and the receiver sensitivity should be large enough. Considering signal fluctuations due to field environments, the fade margin is from 10 dB to 25 dB.  
For the Wi-SUN modems, the antenna gain is 1.5 dBi for the employed quarter-wave monopole antenna and the transmitter power is 23 dBm. Hence, the received power of (9) can be rewritten as \(p=-20\log(d)-5.68\ (\text{dBm})\), for the Wi-SUN case. For example, the received power at a distance of \(d=10\ \text{m}\) without obstacles was approximately \(-25.7\ \text{dBm}\). For practical applications for AMI purposes, a chip-type antenna (Linx Technologies Inc., AEK-916-CHP-ND) can be used. Even though the antenna gain of this chip antenna is 0.5 dBi, practical measurements of the attenuations at a 10 m distance yielded a difference of 5 dB. Hence, when we employ the chip antenna, we should consider a 5 dB compensation. For the ZigBee modem, we use a center frequency of 2.48 GHz and also conduct 1000 MAC ping tests with the package length of 128 bytes to measure the PER performance. We can also use RSSI values to measure the received powers. At \(f=2.48\ \text{GHz}\), the received power of (9) can be rewritten as \(p=-20\log(d)-12.8\) with a monopole antenna of gain 2.2 dBi (Linx Technologies Inc., ANT-DB1-RAF-SMA). At a distance of \(d=10\ \text{m}\), the received power was \(-32.8\ \text{dBm}\), which is less than that of Wi-SUN by 7.1 dB. Hence, even though the antenna gain for the ZigBee modem is better  
Figure 11: ZigBee modem for smart meters (CNU Global Co. Ltd.).  
than the Wi-SUN case, the overall communication performance of the ZigBee modem can be worse than the Wi-SUN case. From (9), we can notice that the slope of \(p\) with respect to the distance of \(\log(d)\) is \(-20\). This slope can be obtained when there are no obstacles and the heights of the antenna modules of both modems are high enough. However, for practical environments, this slope will be less than the theoretical \(-20\).