IX. RESULTS - ACTIVITY TRACKING
In the previous example, we developed a network with its nodes corresponding to different parts of the same body. For the purpose of activity tracking, a body sensor network can be used to aggregate data from different individuals. This study demonstrates two networked smartphones, belonging to separate individuals, recording data over the period of two hours. This study also served the purpose of testing the application’s ability to stream data correctly during everyday use. To form a contrasting set of results indicative of both sedentary and active behaviour, the two individuals were chosen based on the amount of activity they experience on a daily basis. For this experiment, each phone was set to record motion at 10f/s and the study accumulated in excess of 0.5 million points of data (corresponding to 72 000 vector readings and timestamps per individual). In reality, that sampling rate would be reduced to preserve database storage space and smartphone battery [16]. During the recording process, the application sums all angular increments and decrements to extrapolate a coefficient indicative of activity. If the smartphone is rotated 1 degree along each of its three axes, the coefficient of activity will equal 3 (regardless if the rotations are clockwise or anticlockwise). Fig. 9 illustrates a comparison between the two sets of data.