SMARTPHONES WITH ANDROID OS AS MOBILE PROBE
The modern smartphone with an Android operating system (OS) is meant to be a tool for monitoring parameters and network traffic in order to characterize the behavior of cellular communications [10, 11]. The information retrieved can be logged and exported for further post processing analysis. The parameters that are considered to be useful for status monitoring at each time interval are divided in two groups:
Positioning information •GPS info (latitude, longitude and elevation) •User velocity •Moving direction •Precision on monitored data
Network information & operator •Network technology (UMTS, HSDPA) •GSM Cell ID •Signal strength (dBm) •Latency or RTT (Round Trip Time) as Max, Min and median value. •Packet loss
1)Positioning information or geographical data Using the integrated GPS module and relative programming primitives, the geographical data as absolute positioning and moving velocity will be derived. Also particular attention will be given to the precision of the obtained information as the device can be physically not in Line of Sight with GPS satellites, so the obtained data accuracy can be poor. These data is reported during each measuring.
)Network information & operator In this category, we report some useful data for actual 3G network coverage. First, we provide the connected user equipment cell ID and its 3G technology. These data are provided for statistical purposes. The more important and useful information regarding the Received Signal Code Power (RSCP) for UMTS network and Received Signal Strength Indicator (RSSI) for GSM network which are directly related to the data transmitting capacity of the evaluated network. For this purpose, a latency on the transmitted data is measured. These data are considered after sending 10 consecutive ICMP (Internet Control Message Protocol) packets to a web server (www.fti.edu.al is usually used) with a time difference of 20msfor each packet. The difference between transmitting and receiving time for each ICMP packet is used for defining the minimal, maximal and mean Round Trip Time (RTT) [11]. These data are expressed in milliseconds. Smaller these values,better network connectivity in term of network response. Network response loss to ICMP packet data is considered as data loss and is an indicator of the network congestion or network malfunctioning. Smaller this value, better network response is gained.
Regarding the use of this application, a simpler GUI is provided which flow chart is reported in Figure 1. At the startof the application in an Android compatible device (Android OS 4.2 or higher is required) the application will check if thehosting device fulfills all the requirements for loading the signal monitoring tool. At the compatibility control step, the application controls the operating system version, GPS device presence and if it is enabled or not. The application also controls the 3G network activity and connection. If this compatibility control passes successfully, a main window is presented (Figure 2) otherwise an advising window is shown. In the main interface an online network address needs to be provided; the protocol used for measuring purposes should be provided as well. The choice can be between HTTP (Hypertext Transfer Protocol) and ICMP. The preferred protocol is ICMP but in case the provider’s policies result in disabled ICMP protocol, HTTP can be used. At the same interface we need to provide the total sampling points in [1, 1000] range and the sampling time seen as time difference from two consecutive measurements in the [10, 200] range expressed in seconds. Click Here Smaller sampling time can be used for fast moving users and bigger values for slow moving users.
At the end of the monitoring activity, as the flowchart shows (Fig. 1), a saving window will prompt the user for successful data save. We will arrive at the same result if we use the STOP button which will save the current measured information at current state without measuring all the imposed sampling points.
