# GPRS Sensor Node Battery Life Span Prediction Based on Received Signal Quality: Experimental Study
## 4 Data Analysis and Discussion
### RSSI vs. Current Consumption  
Researchers found that when a GSM module in a GSM network has low signal quality, the module will put a lot of effort into trying to get better signal reception; this will make the module consume more power [9; 37]. The following Tables 4-9 show the impact of the received signal quality on the current consumption of the GSM module. Data have been recorded in six different locations. For each location, we tried to make an average for the consumed current.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **No** & **Time [s]** & **GSM-Current [A]** & **GPRS-Current [A]** & **RSSI [TA]** & **RSSI [dBm]** \\ \hline
1 & 0 & 0.014 & 0.009 & 31 & \(-\)53 \\
2 & 0.5 & 0.016 & 0.008 & 31 & \(-\)53 \\
3 & 1 & 0.011 & 0.008 & 31 & \(-\)53 \\
4 & 1.5 & 0.015 & 0.008 & 31 & \(-\)53 \\
5 & 2 & 0.021 & 0.005 & 31 & \(-\)53 \. &. &. &. &. \. &. &. &. &. \\
172,800 & 86,400 & 0.006 & 0.009 & 31 & \(-\)53 \\
**Average** & & **0.0065** & **0.0088** & **31** & \(-\)**53** \\ \hline \hline \end{tabular}
\end{table}
Table 6: Current consumption in location 3, RSSI = \(-\)53 dBm.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **No** & **Time [s]** & **GSM-Current [A]** & **GPRS-Current [A]** & **RSSI [TA]** & **RSSI [dBm]** \\ \hline
1 & 0 & 0.011 & 0.008 & 19 & \(-\)75 \\
2 & 0.5 & 0.007  
The GSM currents were recorded when the module was connected to the network and by disconnecting the cable which links the module to the microcontroller. At this time, the module was not able to receive AT command from the microcontroller.  
The graphs for all the six locations show that the GSM current is almost constant and that the GPRS current changes according to how often data are transmitted.  
The results from measurements taken from six different locations show that if a GPRS sensor node is located in a place with poor signal quality, the node will consume more current.  
Among these six locations, location 2 was the one with poor signal quality (\(-83\) dBm) (Figure 13, Table 5), the node was consuming 17 mA, while location 3 was the one with excellent signal reception (Figure 14 and Table 6), where the sensor node was consuming around 9 mA. Considering location 3 and location 6 with \(-53\) dBm and \(-63\) dB Figure 14 and Table 9) respectively, from those two locations, the results from our experiments show that when the RSSI value reduces with 1  
Figure 16: Current consumption in location 4: RSSI \(=-73\) dBm.  
Figure 15: Current consumption in location 1: RSSI \(=-75\) dBm.  
We can generally observe that on each graph (Figures 13-18), there is an overshoot each 20 s, at this time the module was receiving a GPRS AT command to send data to a remote database. On the same graphs, we can observe that the GPRS protocol consumes more power than GSM protocol. One of the useful services of GSM protocol is transmission of voice which can go to a maximum of 14.4 kbit/s. The GPRS protocol was one of the major developments of GSM network which can support packet switching techniques to accommodate high speed data rate and fast data communication which can go up to 170 kbit/s [38]. In our application there is no voice transmission as there is no microphone or/and speaker connected to the module. However, the module is transmitting some data to a remote database using GPRS protocol; this is why the module consumes more power when it is used in GPRS protocol. It has even been proven by [PERSON] et al. [39] that the power consumption increases with data rate.  
Figure 17: Current consumption in location 5: RSSI = \(-65\) dBm.  
Figure 18: Current consumption in location 6: RSSI = \(-63\) dBm.  
The results from Table 10 consolidate all results from six locations and they are plotted in Figure 19; the TA values of RSSI have been converted using the Table 3.